release: v0.5.0

[bug-ops]

Summary

• Bump version from 0.4.0 to 0.5.0 across the workspace
• Consolidate CHANGELOG.md [Unreleased] entries into the [0.5.0] section, merging duplicate per-PR bullets and correcting a stale PR reference (retried transient LSP errors (ContentModified/ServerCancelled) log at ERROR severity before the retry succeeds #392 -> fix(lsp): log retried transient errors at warn, not error #401)
• Update specs/ to reflect code shipped since v0.4.0 (structured tool output, tool_prefix, ContentModified retry, LspTransport signature, non_exhaustive enums, rmcp 3.2.0), fix missing constitution wikilinks, mark bridge/003 as superseded
• Document the HTTP transport authentication gap in docs/user-guide/configuration.md
• Note structured tool output for 4 MCP tools in README.md

Checklist

• Version updated in all manifests (workspace.package.version + internal mcpls-core dependency version)
• CHANGELOG.md has release section with date
• README reflects new version
• All CI checks pass locally (fmt, clippy, nextest, rustdoc)
• Ready for tagging after merge