fix(runtime): route runtime filesystem commands by resolved execution host (#18325)

`ResolvedRuntimeFileTarget` carried `connectionId?: string` and no host id, so
`undefined` spelled three different answers at once — "runtime: host", "unresolved"
and "genuinely local". Its sole resolver read `store.getRepo(worktree.repoId)?.connectionId`
and never looked at `worktree.hostId`, which outranks every repo row, so one
arbitrarily chosen row decided the execution host for ~30 filesystem dispatches.
This is #18307's defect in the same file family; it was deliberately left out of
that PR rather than doubling an already-36-site diff.

The target now carries `executionHostId: ExecutionHostId` (never null, never
optional), resolved through `resolveWorktreeHostRouting` — the same adapter #18307
added — and dispatched through #18296's `resolveFilesystemRouteForHost`. Dispatch
sites call `requireRuntimeFileProvider`, where `null` means exactly one thing: the
host is `local` and the read happens here.

Four answers that used to collapse into one:

- `ssh:x` with a rival row on `ssh:y` — routes to x. Previously the first row won.
- `local` with a surviving `connectionId` — a row contradicting itself; no SSH
  connection is handed out.
- `runtime:<env>` — throws `ExecutionHostNotDispatchableError`. Its repo row's
  connection names a target in the *server's* namespace; reading it here reaches a
  same-named target on this client.
- rival rows disagreeing with no worktree host — `worktree_execution_host_unresolved`,
  matching the launch and Git paths rather than guessing a row.

Two further reads stop degrading. `assertRuntimeFileMutationExpectation` recomputed
the host from `connectionId`, so a client's host expectation could pass against a
host the workspace never named; it now compares the resolved host. And the
cross-workspace terminal tap coalesced `knownWorkspaceTarget?.connectionId ??
connectionId`, so a sibling workspace resolved as `local` inherited the origin
worktree's SSH target and statted a local path on the remote box; a non-optional
host id replaces rather than coalesces.

An unreachable SSH host still throws `SSH_FILESYSTEM_PROVIDER_UNAVAILABLE_MESSAGE`;
loss of contact is never evidence of locality (docs/reference/ssh-execution-boundary.md).
Quick-open listing and path search keep degrading to empty for an unreachable host —
that is a false negative, not a local answer — and now do so only for a host that
really is remote.

The whole `runtime-file-commands-*` family carries `@ts-nocheck` from a mechanical
class split, so removing the field could not raise the compile errors that made
#18307 safe. `runtime-file-command-target.ts` is deliberately checked, and a ratchet
test stands in for the errors the family cannot produce.

No wire change: `ResolvedRuntimeFileTarget` is main-process internal, and the SSH
watcher-release and grant keys are byte-identical to before.

docs/reference/ssh-execution-boundary.md

@@ -13,7 +13,7 @@ Two consequences, both non-negotiable:
 
 The vocabulary is fixed: **`live` / `unverifiable` / `exited`**, taken from the incumbent `UnstoppedPtyVerdict`. Do not introduce synonyms, and never collapse `unverifiable` into either neighbour. `exited` requires positive evidence of absence from the host that owns the process; a transport failure can only ever produce `unverifiable`.
 
-Rule 1 is stated at `src/main/source-control/repo-default-branch.ts:76-78`, `src/main/repo-worktrees.ts:45-48`, `OrcaRuntimeService.probeWorktreeDrift` in `src/main/runtime/orca-runtime.ts`, and `src/renderer/src/lib/connection-context.ts:22-24`. It is enforced throughout `src/main/runtime/orca-runtime-git.ts` by `requireRuntimeGitProvider` in `src/main/runtime/runtime-git-command-target.ts`, which routes on the target's resolved `executionHostId` rather than on a repo row's `connectionId`: it throws `SSH_GIT_PROVIDER_UNAVAILABLE_MESSAGE` when an SSH host has no registered provider, throws `ExecutionHostNotDispatchableError` for a `runtime:` host this process does not execute, and returns `null` only for `local`. Grep those two names for the current call sites rather than trusting a count.
+Rule 1 is stated at `src/main/source-control/repo-default-branch.ts:76-78`, `src/main/repo-worktrees.ts:45-48`, `OrcaRuntimeService.probeWorktreeDrift` in `src/main/runtime/orca-runtime.ts`, and `src/renderer/src/lib/connection-context.ts:22-24`. It is enforced throughout `src/main/runtime/orca-runtime-git.ts` by `requireRuntimeGitProvider` in `src/main/runtime/runtime-git-command-target.ts`, and throughout the runtime filesystem commands by `requireRuntimeFileProvider` in `src/main/runtime/runtime-file-command-target.ts`. Both route on the target's resolved `executionHostId` rather than on a repo row's `connectionId`: they throw the provider-unavailable message when an SSH host has no registered provider, throw `ExecutionHostNotDispatchableError` for a `runtime:` host this process does not execute, and return `null` only for `local`. Grep those names for the current call sites rather than trusting a count.
 
 `src/main/runtime/unstopped-pty-verification.ts:12-16` is the reference implementation of rule 2: it keeps `live` / `unverifiable` / `exited` as three distinct verdicts, and treats "we could not ask" as its own answer.