MCP upgrade 4/6: Bounded project context

[Lauritz-Timm]

Part of the six-phase full MCP service upgrade.

Why

Clients need bounded project context through the MCP resource model without unbounded reads or machine-specific assumptions.

What

• Adds exact-topic bounded reads.
• Exposes project context as an MCP resource.
• Covers resource limits and boundary behavior.

Dependency

Direct prerequisite: Phase 2 — Revision-aware core service. This phase is independently mergeable after Core.

Verification

• Formatting and strict all-target/all-feature Clippy passed.
• Integrated Core, MCP, and Store suites passed.
• The final isolated candidate evaluation passed 294/294 scenarios in each of two portable roots with normalized equality.