fix(hook): resolve Claude transcript by session id

[rNoz]

Summary

• resolve Claude transcripts by the metadata session ID across project directories instead of assuming the current working-directory slug
• fail closed when precise or relevant invalid metadata cannot safely resolve a transcript, allowing mtime heuristics only when metadata is unavailable
• preserve /clear handling while avoiding concurrent registered sessions

Validation

• bun test apps/hook/server/session-log.test.ts (126 passed)
• bun test apps/hook/server --timeout 15000 (253 passed)
• PATH="$PWD/apps/hook/node_modules/.bin:$PATH" bun run typecheck
• git diff --check upstream/main

Closes #985.

[rNoz]

@backnotprop I hope you like it :)