Cross-service linker plumbing (PR 1/5)

[Shidfar]

Summary

Pure plumbing for cross-service protocol linking — the framework only, no protocol linkers yet. Splits the 24K-line bundle from #295 into 5 reviewable PRs per your guidance; this is the foundation.

What this adds

• src/pipeline/servicelink.h — shared types (endpoint, endpoint-list, config), 14 protocol edge constants, helper inlines
• src/pipeline/pass_servicelinks.c — pipeline pass that loads .cgrconfig, iterates a (currently empty) LINKERS dispatch table. Each protocol linker registers its row in PR 2.
• src/mcp/mcp.c — registers the cross_project_links MCP tool and its handler. The handler returns "No cross-project links found" since no writer exists yet — wired in PR 3 and migrated to the unified storage in PR 5.
• src/store/store.c — adds the protocol_endpoints table to the project schema
• tests/test_endpoint_registry.c — covers cbm_sl_endpoint_list_* helpers
• tests/test_endpoint_persistence.c is intentionally not here — it tests cbm_persist_endpoints which lives in PR 3

What's NOT in this PR

The empty LINKERS table makes pass_servicelinks a no-op until PR 2 lands the 14 protocol linker .c files and restores the full 14-row dispatch. The MCP tool exists but answers empty until PR 3 wires the writer, and PR 5 rewires the reader to the unified storage.

Note on #295's URL flag

PR #295 substituted DeusData → hodizoda across server.json / scripts/setup*.sh / SECURITY.md / etc. My local fork was rebased onto fresh upstream after that comment and the URL-substitution commits were dropped in the process; this PR (and the 4 stacked behind it) carry none of those changes — install paths, registry URLs, and security-audit allowlists all remain pointed at DeusData/codebase-memory-mcp. Verified with git diff upstream/main -- server.json scripts/setup*.sh scripts/security-*.sh scripts/security-allowlist.txt SECURITY.md README.md CONTRIBUTING.md docs/index.html .github/workflows/release.yml returning empty.

Test plan

• ./scripts/test.sh passes (3620/3620, ASan + UBSan)
• Builds in isolation — no undefined references to protocol-linker symbols

PR stack

This is the bottom of a 5-PR stack. The remaining PRs (drafts):

• PR 2 (draft): 14 protocol linkers (graphql/grpc/kafka/sqs/sns/ws/sse/pubsub/rabbitmq/eventbridge/mqtt/nats/redis_pubsub/trpc) — wired into the dispatch table
• PR 3 (draft): cross-repo pass + community detection + MCP cross_project_links integration
• PR 4 (draft): HTTP cross-project edges (4-signal endpoint registration)
• PR 5 (draft): storage unification + incremental parity + MCP reader migration

Each will be un-drafted as the chain merges.