feat(observability): record what already reports before a catch removes it

[MajorLift]

Summary

• Adds observability/knowledge/error-reporting-paths.md. Sentry.init in setupSentry.ts never sets defaultIntegrations: false, so the browser SDK merges globalHandlersIntegration() in and an uncaught throw or unhandled rejection already reports. A .catch(console.debug) on such a path deletes the only report rather than degrading gracefully, so the pair is reported versus silent rather than crash versus degrade.
• Adds a short section to instrumentation's extension overlay pointing at it, since that skill is where what-reaches-Sentry already lives.
• tsc-blindspots keeps its own "Silent failure modes deserve their own pass" passage and gains one line naming the prior question, which is whether the path reported at all. The knowledge file carries that passage's weighting rule as well, so an observability reader gets it without following a cross-domain link.
• Trims tsc-blindspots' description from 1341 characters to under the 1024 the repo lints. It is the only skill on main currently over budget: fix: shorten skill descriptions over the 1024-character operator limit #158's sweep merged three days after feat: Adds typescript domain with authoring, migration skills #167 introduced it, and CI lints changed files only, so it stayed dormant until this PR touched the file.

Test plan

• node --test test/*.test.mjs passes 72 of 72, up from 71 as the new knowledge file is collected.
• node .github/scripts/lint-skill-entry.mjs on both touched skills reports 0 errors. Two warnings for a missing recommended section are pre-existing.
• Every skill.md under domains/ is within the description budget after this change.
• Both permalinks in the knowledge file return 200 against a bogus-sha control returning 404.