fix: correct 4 documentation inaccuracies found by docs-validation suite

[beonde]

Summary

Fixes 4 documentation inaccuracies discovered by the automated docs-validation test suite (capiscio-e2e-tests/docs-validation/).

Findings & Fixes

1. CLI --version output format (Low severity)

• Docs said: capiscio/X.Y.Z (darwin-arm64)
• Actual: capiscio version X.Y.Z (commit: <hash>)
• Files: getting-started/validate/2-install.md

2. Missing protocolVersion in agent card examples (High severity)

• Agent card examples that readers copy-paste would fail validation with MISSING_PROTOCOL_VERSION error
• Files: getting-started/validate/3-validate.md, getting-started/complete-workflow.md, assets/samples/agent-card.json, assets/samples/agent-card-full.json

3. iss claim not present in dev_mode (Medium severity)

• Docs showed iss in example output, but verify_inbound() in dev_mode only returns iat, exp, bh
• Code examples referencing claims['iss'] would raise KeyError
• Files: getting-started/secure/1-intro.md, getting-started/secure/2-sdk.md, getting-started/secure/3-guard.md
• Fix: Updated example outputs, added note clarifying iss is production-only, used .get('iss', 'dev-mode agent') fallback

4. Dev mode trust store behavior (Medium severity)

• Verification table claimed trust store checking rejects untrusted keys
• In dev_mode=True, verify_inbound() actually accepts any valid Ed25519 signature
• Trust rejection only works with configured trust store or CapiscioMiddleware
• Files: getting-started/secure/3-guard.md
• Fix: Added warning admonition clarifying dev_mode behavior

Validation

All findings discovered and verified by the capiscio-e2e-tests/docs-validation/ test suite:

• 48 tests pass, 7 skipped (MCP guard not installed, badge PoP requires DID setup)
• Sub-millisecond SDK latency confirmed: sign p50=0.118ms, verify p50=0.111ms, headers p50=0.075ms

[github-actions]

✅ Documentation Build Successful

The documentation build completed successfully and passed validation checks.

• ✅ Build completed without errors
• ✅ Critical files present (index.html, sitemap.xml, robots.txt)
• ✅ Link validation completed

This PR will deploy to dev-docs.capisc.io when merged to main.