fix(settings): validate PORT instead of silently defaulting to 3000

[pedrofrxncx]

Follows #5123, which hardened DATABASE_POOL_MAX to reject malformed values via a new toPositiveIntegerOrDefault helper instead of silently defaulting. port in the same resolveConfig function still had the old pattern: Number(flags.port) || Number(envVars.PORT) || 3000.

Payoff: a typo'd or malformed PORT (e.g. PORT=abc, PORT=-1, PORT=0) currently falls back to 3000 with zero warning, so a deploy silently binds to the wrong port instead of failing fast at startup — exactly the class of bug #5123 just fixed for the pool-size setting.

Fix: reuse the existing toPositiveIntegerOrDefault helper for port, keeping the --port flag > PORT env var precedence, defaulting to 3000 only when neither is set, and throwing PORT must be a positive integer otherwise.

Reviewer check: cd apps/mesh && bun test src/settings/resolve-config.test.ts

Verified locally: bun run fmt, bunx tsc --noEmit (apps/mesh workspace), and the targeted test file above (32 pass). Full CI runs the rest.

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Summary by cubic

Validate PORT in mesh config and fail fast on invalid values instead of silently defaulting to 3000. Keeps --port > PORT precedence and only defaults to 3000 when both are unset.

• Bug Fixes
  • Use toPositiveIntegerOrDefault("PORT", flags.port || envVars.PORT, 3000) in resolveConfig.
  • Throw a clear error for invalid values (e.g., "abc", "0", "-1", "1.5", "Infinity").
  • Add tests for defaulting, env/flag precedence, and invalid inputs.

^{Written for commit ce6fcc3. Summary will update on new commits.}