v1.3.4 — security hardening (XSS invariants + dep audit)

Security

• Restored the textContent-only invariant documented in THREAT_MODEL.md §C. Two webview callsites that were using static-string innerHTML (the empty-state heading at media/main.js:186 and the pin-button SVG at media/main.js:236) now build their DOM via createElement/createElementNS. Neither was an exploitable XSS — both strings were literals — but the invariant matters for static analysis and future-proofing.
• Documented the markdown-preview rendering surface as new THREAT_MODEL.md §F. The preview pane introduced in 1.3.0 sends marked.parse(body) into innerHTML, which is safe under the existing CSP (script-src 'nonce-X' webview.cspSource; default-src 'none'; img-src webview.cspSource data:) — that CSP blocks every JavaScript sink raw markdown HTML could expose (inline <script>, on* handlers, javascript: URIs, remote <img>, <iframe>). Added an inline comment at media/main.js:478 so future contributors don't add a sanitizer reflexively or weaken the CSP without re-evaluating §F.
• Bumped @typescript-eslint/eslint-plugin and @typescript-eslint/parser from ^6.0.0 to ^8.0.0. Resolves all 6 high-severity npm audit findings (transitive on @typescript-eslint/typescript-estree). v8 requires ESLint ≥8.57 and Node ≥18.18, both satisfied.
• Hardened .gitignore with patterns for .env, .env.*, credentials.json, serviceAccountKey*.json, *.pem, *.key. The extension stores no credentials, so this is purely defense-in-depth against accidental check-ins of unrelated files in dev workspaces.

Notes (not changed)

The remaining 5 moderate npm audit findings (@vscode/vsce → @azure/identity → @azure/msal-node → uuid, plus ovsx) are dev-only and never ship in the VSIX. npm audit fix --force would downgrade ovsx from 0.10.11 to 0.9.4, losing features. Accepted risk.