feat: wire CodeGraph into CoDev Code via custom target or config shim

[quickbeard]

Summary

codegraph has no built-in installer target for CoDev Code. This PR wires the fork anyway, structured so that adoption of upstream codegraph PR #1459 (custom installer targets) is fully automatic when it lands:

• Path A (custom target) — setupCodegraph probes the installed binary with the read-only codegraph targets list. When custom targets are supported, it registers the codev spec (codegraph targets add, opencode family, appName: codev) and appends codev to the single codegraph install CSV.
• Path B (config shim) — on today's binaries, wireCodevCodeMcp() writes the same mcp.codegraph entry into ~/.config/codev/codev.json(c) directly: surgical jsonc-parser edits (comments and sibling MCP servers survive), idempotent (an already-correct entry writes nothing), and it refuses malformed files rather than risk corrupting them.

Both paths produce byte-identical on-disk config in the same file, so a machine can flip between them run-to-run invisibly. Since codev-hub always npm i -gs the latest codegraph before wiring, Path A activates machine-by-machine the moment upstream releases — no codev-hub release, no user action. Once the released codegraph floor supports custom targets, Path B and the probe are a pure code deletion (marked in AGENTS.md).

Also fixes a live clobber bug

configureOpenCodeKind whole-file-replaces its config and runs on every gateway-key auto-refresh (ensureFreshGatewayKey) and codevhub model switch — silently dropping any mcp entries wired after install. That already bites OpenCode + CodeGraph users today. It now carries the existing top-level mcp map across the rewrite (best-effort, object-valued maps only). The map never lands in *.backup, so restore still returns the true pre-CoDev state.

Supporting changes

• Gating: the three codegraphTargets(...).length > 0 gates (Install row, config mode's CodeGraph step, finalize frame) become codegraphEligible(tools), which includes codev-code. The always-on flagship selection previously skipped installing the codegraph package entirely — and the new wiring would otherwise reference a missing binary.
• Remove: runCodegraphRemoval sweeps the fork's mcp.codegraph entry after codegraph uninstall (no-op when a custom-target-aware uninstall already removed it; drops an emptied mcp wrapper; sibling servers and user-owned files preserved per the kept-live gate).
• CodegraphTarget gains "codev" → "CoDev Code" so the finalize message names it on both paths.

Testing

• 18 new tests: probe/register call shapes; all four setup paths (custom target, shim, codev-only, registration-failure fallback); shim idempotency, comment/sibling preservation, malformed-file refusal; unwire behavior; mcp carry-over for OpenCode and the fork; the remove sweep on a user-owned config.
• pnpm fix, pnpm typecheck, pnpm test (968 passed), pnpm build && node dist/index.js --version all green.

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