fix: resolve 11 important bugs from deep code review

[jackwener]

Summary

• I1: Log pre-navigation failures in debug mode instead of silently swallowing (execution.ts)
• I2: Validate env var timeout values with NaN/negative guard (runtime.ts)
• I4: Guard indexOf returning -1 for unknown strategies in cascade (cascade.ts)
• I5: Fix shouldReplaceManifestEntry returning true for same-type entries — was causing unnecessary overwrites (build-manifest.ts)
• I6: Prevent infinite loop in parseTsArgsBlock cursor advancement (build-manifest.ts)
• I7: Skip redundant Page.enable CDP calls on repeated goto() (cdp.ts)
• I8: Fix wait({time:0}) being treated as falsy due to if (options.time) check (page.ts)
• I10: Warn when cookiesFile path doesn't exist before falling back to browser cookies (download/index.ts)
• I11: Sanitize tab/newline chars in cookie name/value to prevent Netscape format corruption (download/index.ts)
• I12: Use DEFAULT_DAEMON_PORT constant instead of hardcoded port in error message (mcp.ts)
• I15: Log npm install failures in plugin lifecycle instead of swallowing silently (plugin.ts)

Test plan

• TypeScript typecheck passes (tsc --noEmit)
• All 223 unit tests pass (npm test)
• Manual verification of edge cases (NaN env vars, time:0 wait, tab-in-cookie)

🤖 Generated with Claude Code

[jackwener]

Reviewed and merged. I re-ran npm run typecheck and npm test locally; both passed. The only non-blocking note is that same-type duplicate manifest entries are still "first one wins" and silent, but that does not block this PR.