[#120] Move the schema documentation to where it is useful

[SkowronskiAndrew]

Summary

Fixes #120.

SQLite only keeps the text of the CREATE statement itself in sqlite_master, so a comment placed
above a statement is discarded. All 58 comment lines documenting the core schema in Init.sql
were above their statements, so none of them reached a produced database: .schema objects showed
bare column names, and anyone working from a .db artifact never saw the documentation.

This takes both halves of the fix offered in the issue. Concise key facts move inside the CREATE
statements, where SQLite preserves them verbatim, so a produced database is self-describing. The
detailed prose moves into the documentation, which has shipped in the release zip since #118, so it
travels with the binary. Every comment outside a CREATE is gone, so the old practice stops rather
than being repeated by the next table.

Only facts that are needed to write a correct query and are not guessable from the column name went
into the schema, for example that serialized_files.archive and objects.game_object hold ''
rather than NULL, that refs.referenced_object can be a dangling_refs.id, and that --skip-crc
sets every crc32 to 0. .schema serialized_files now reads:

CREATE TABLE serialized_files
(
    -- One row per SerializedFile analyzed.
    id INTEGER,
    archive INTEGER,    -- archives.id, or '' when the file is not inside an archive
    name TEXT,          -- on-disk name, usually hash-based: CAB-<hash>, BuildPlayer-<scene>, levelN
    PRIMARY KEY (id)
);

No table, view or column changed — verified mechanically that all 15 changed .sql files are
byte-identical to their previous versions once comments are stripped. PRAGMA user_version therefore
stays at 7; bumping it would falsely signal an incompatibility to find-refs.

Changes

SQL resources

• Init.sql: all 58 comments outside CREATE statements removed. Table-level notes and per-column
  notes added inside the parentheses; each of the 7 views gained a one-line purpose comment as the
  first line of its body (5 of them had no comment at all before). The INSERT INTO types comment
  could not survive on its own, so the -1 Scene sentinel is documented on types.id instead.
• AssetBundle.sql had the identical bug — 19 lines of good comments, all discarded. Same treatment.
• The 13 ContentLayout*.sql files were half converted: good in-paren column notes plus a prose
  block above each statement that was thrown away. The prose blocks are gone and anything
  query-critical that lived only there (e.g. why serialized_file is NULL for a layout-only
  analyze) was promoted into the parentheses.
• ContentLayoutViews.sql and ContentSummary.sql: per-view comments moved inside the view bodies.
• ContentLayoutIndexes.sql keeps one comment outside the statements, trimmed to the "why late"
  rationale. CREATE INDEX has no body to hold a note, and that comment explains the code rather
  than the schema.
• AGENTS.md records the convention so new .sql files follow it.

Documentation

• New Documentation/analyzer-schema.md: the schema reference, in one uniform format
  (| Column | Type | Description | per entity, plus an at-a-glance index). Replaces the four
  different styles previously in use across the schema pages.
• Documentation/analyzer.md was 81% schema reference; it is now a 76-line overview (intro, a map of
  where each part of the schema is documented, and the Advanced/extending sections).
• Documentation/contentlayout-database.md reformatted to the same markdown-table shape, absorbing
  the prose evicted from the ContentLayout*.sql files.
• serialized_files, types, property_names and property_types gained documentation they never
  had — the SerializedFile naming rules per build pipeline (CAB-, BuildPlayer-, levelN) existed
  only in a discarded Init.sql comment.
• The schema version history moved out of the Init.sql comment into a markdown table on the new
  page; AGENTS.md points the bump rule at it.
• agent-guide.md told agents that "the produced database's schema shows bare table definitions",
  which this change makes false. Rewritten.
• Referrers retargeted so links promising a schema reference land on the new page.

Incidental fixes

• Analyzer/Properties/Resources.resx: Init.sql and Finalize.sql were declared Windows-1252
  while the other 49 .sql entries are utf-8. Both date from the initial commit and there is no
  purpose to it; all .sql files are pure ASCII, which decodes identically under either encoding, so
  the switch to utf-8 is a no-op on current content and removes a trap for future comment edits.
• The /* TABLE DEFINITION: */ blocks in the nine Commands/SerializedFile/*.cs classes hand-copied
  the DDL and had to be kept in sync manually. They are replaced with a one-line pointer to the
  owning .sql file. The drift was already real: AddPreloadDependency declared
  PRIMARY KEY (object, dependency), which the actual DDL has never had.
• Nine pre-existing broken documentation links fixed, found by a link check written for this PR.
  Notably analyzer.md described an IWriter interface that no longer exists in the codebase.

Testing

• dotnet build -c Release — clean, 0 warnings.
• dotnet test -c Release — full suite green: 787 passed, 0 failed (Analyzer.Tests 62,
  UnityFileSystem.Tests 435, UnityDataTool.Tests 290). Any .sql syntax error fails essentially
  every analyze test at Begin(), so this is the real regression net.
• Manual verification on a real database: ran analyze against TestCommon/Data/AssetBundles and
  against the ContentDirectory build in TestCommon/Data/LeadingEdgeBuilds, then confirmed with
  sqlite3 ... ".schema <table>" that the notes are present and readable for core tables,
  AssetBundle tables, ContentLayout tables and views; that queries against object_view and
  view_breakdown_by_type still work; and that PRAGMA user_version still reports 7. Re-ran after
  the ResX encoding change to confirm the resource still loads.
• Verified all 15 changed .sql files are byte-identical ignoring comments, so the schema itself is
  untouched.
• Verified every internal documentation link and anchor across all 26 markdown files resolves
  (0 problems), since there is no CI link checker.
• Verified all .sql files are pure ASCII and that the only remaining comment outside a CREATE
  statement is the intended ContentLayoutIndexes.sql one.

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