chore(devtools): record bitty-core jurisdiction + fix stale docs + sync trace accounting semantics

[Xuepoo]

Priority: P2 | Area: docs | Labels: chore,P2,area:docs | Milestone: v0.1.0 | RFC: none | Task: CTX-0075

Closes #130

Docs-only governance sync for bitty-devtools under bitty-core jurisdiction. No code behavior changes.

Changes

• repo.toml — owner TBD -> bitty-core, matching the workspace map (workspace.toml already records bitty-core). This carries the uncommitted local edit from the workspace restructure.
• AGENTS.md — records management by the bitty-core commander (terminal-platform jurisdiction, alongside bitty and bitty-terminal-docs) while keeping the boundary sentences (core debug/command contracts -> bitty; canonical architecture/security/public behavior -> bitty-docs); applies the scratch-wording unification hunk (ephemeral under /tmp/bitty/, durable under this repository's recording/); replaces the blanket pre-implementation claim only where stale against merged code (tracing phases 1/2, inspect-only watch mode, live-socket fixtures) with Implemented-only wording. No Verified/Compatible upgrade.
• README.md — new "Trace accounting semantics (Implemented, CTX-0053 / CTX-0054)" section syncing the client trace helper clarification in bitty-terminal-docs specifications/devtools-rfc.md (merged a205c17, CTX-0026): retained redacted logical UTF-8 export-byte accounting (not heap/filesystem occupancy), independent per-record normalization with a leading U+FEFF preserved as data, effective min(trace maxBytes, retention maxBytes) rejection with one counted drop and unchanged retained state, opaque raw append vs typed stream coalescing, and fetchTraceChunk pagination on retained UTF-8 byte offsets.
• CHANGELOG.md — docs-only Changed entry recording the same semantics sync.

Claim verification (read-only against current code)

Each README claim was verified before writing, not copied from the RFC:

• src/tracing.ts appendToTrace (redact -> per-record UTF-8 normalize -> byte length), appendStructuredEvent (serialized JSON bytes), both bill min(rec.options.maxBytes, rec.retention.maxBytes), increment drops once on rejection, and leave retained bytes/chunks/events/previews unchanged.
• src/tracing.ts fetchTraceChunk: rejects non-safe-integer/negative offsets and non-UTF-8-boundary offsets, returns the remaining bytes of the addressed stored chunk, computes continuation from actual retained byte lengths, and asserts preview-equals-export.
• crates/devtools-client/src/tracing.rs append_to_trace/append_structured mirror the same accounting; tests raw_retention_matches_utf8_model, structured_retention_matches_serialized_bytes, and retained_redaction_is_measured assert retained state is unchanged on rejection.
• tests/tracing.test.ts covers BOM/U+FEFF preservation and per-record normalization ("\uFFFD\uFFFD\uFEFFéz"), UTF-8 boundary offsets, continuation, and raw-vs-typed coalescing.

Evidence

• just check green: prettier 3.9.6 check, markdownlint-cli2 0.23.1 (0 issues), tsc --noEmit, bun test (444 pass / 0 fail), cargo fmt --check, cargo check --locked, cargo clippy -D warnings, cargo test (79 + 20 pass).
• actionlint .github/workflows/*.yml clean.
• act -n -W .github/workflows/ci.yml --action-offline-mode: all three jobs (Quality gates, actionlint, Fuzz smoke) dry-run succeeded. Without --action-offline-mode, act dry-run fails resolving the taiki-e/install-action remote (act network limitation); workflows are unchanged by this PR.

Trust boundaries

Docs-only: no protocol, wire, or code behavior change. Terminal and trace content remains untrusted observation data; no secrets, captures, or host-specific paths added.

Residual risks / follow-ups

• origin/main bun.lock is stale relative to package.json (@types/bun/bun-types 1.4.0 vs pinned 1.4.2, carryctx 0.11.2 vs 0.11.4), so bun install --frozen-lockfile fails on a clean clone. Untouched here (docs-only scope); needs its own chore task.
• The act dry-run online action-fetch failure above is an act limitation, not a workflow defect; actionlint and offline dry-run are clean.

Task: CTX-0075