chore(security): remove dead reasoning-offload modules flagged in #1114 (#1132)

The managed-reasoning removal (e5897d03) stripped the CLI/MCP wiring but,
despite its stated intent, left the offload modules and their test suite
behind. The dead code still shipped compiled inside the platform bundles,
and its Windows browser-opener was flagged by a security report (#1114)
for routing the login URL through `cmd /c start`, where cmd re-parses
shell metacharacters. Unreachable since 2026-06-20 and never wired in any
tagged release — but delete it for real: src/reasoning/ (config,
credentials, login, reasoner), __tests__/offload.test.ts, the now-inert
CODEGRAPH_OFFLOAD_DISABLE guard in dynamic-boundaries.test.ts, and the
stale reasoner reference in the FILE_SECTION_PREFIX comment.

Closes #1114

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

CHANGELOG.md

@@ -12,6 +12,7 @@ and adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 ### Fixes
 
 - Lua and Luau method calls with capitalized names (`obj:Method()` — the standard Roblox convention) now link to the right method. Because Lua's method-call syntax looks identical to a Luau type annotation, a capitalized call like `lg:Log()` was misread as declaring the variable's type, so whenever two or more classes shared a method name (`Init`, `Update`, `Destroy`, …) the call was silently dropped from callers, impact/blast-radius, and flow traces. Lowercase method names were unaffected. Thanks @inth3shadows for the precise root-cause analysis and repro. (#1124)
+- Removed dead code left behind by the discontinued managed-reasoning feature. Its `codegraph login` flow was unplugged before ever shipping in a release, but the unused module still shipped inside the platform bundles, and a security review flagged its Windows browser-open step (it routed the login URL through `cmd`, which would have been unsafe had the flow ever been wired back up). The leftover module and its tests are now fully deleted. Thanks @inth3shadows for the report. (#1114)
 
 ## [1.2.0] - 2026-07-02