Add auto-resolve for names in server_id/site_id across all MCP calls (#75)

[titouanmathis]

Closes #75

Adds transparent name→ID resolution in executeToolWithCredentials() middleware. When server_id or site_id contains a non-numeric string, the system automatically resolves it to the matching server/site ID before routing to handlers.

• Single exact match: resolves silently
• Multiple matches: returns error listing candidates
• No matches: returns descriptive error
• Skipped for resolve action (which handles its own name resolution)

Rebased onto main after #72 was merged.

---

Supersedes #77 (auto-closed when target branch was deleted).

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.80%. Comparing base (56ae8a9) to head (97b8ac4).
⚠️ Report is 2 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #81   +/-   ##
=======================================
  Coverage   99.80%   99.80%           
=======================================
  Files         223      224    +1     
  Lines        3596     3629   +33     
  Branches      833      824    -9     
=======================================
+ Hits         3589     3622   +33     
  Misses          7        7           

Flag	Coverage Δ
unittests	99.80% <100.00%> (+<0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.