[Feature]: Name remote terminal sessions in the Resource Manager instead of showing raw pids

### Problem

With the Resource Manager showing remote runtime hosts (#15984 / #16000), sessions on a remote host render as `pid 712692` instead of a terminal name:

```
docs-pass · REMOTE 1.3% 95.7 MB
pid 712692 1.3% 86.3 MB
pid 713986 0.0% 9.4 MB
```

Local rows are unaffected, and remote rows are fine *while you have that workspace open* — the label resolves from the client's own tab. The gap shows up exactly when the panel is most useful: looking at a host whose workspaces you are not currently viewing, which is the reason to look at another host's resource usage in the first place.

### Why

`resolveSnapshotSessionLabel()` in `mergeSnapshotAndSessions.ts` resolves a name by walking this client's tab store via `paneKey`, then falls back to `pid `. For a remote host there is often no local tab bound to that session, so the fallback is all that is left.

The remote payload cannot help either: `SessionMemory` in `src/shared/process-stats-types.ts` carries only `sessionId`, `paneKey`, `pid`, `cpu` and `memory`. `diagnostics.memory` never had a reason to include a title, because until now the only consumer was the machine that already owned the tabs.

For local sessions the name comes from `pty.listSessions()`, whose rows carry `title` and `cwd`. That list describes this machine only, so it says nothing about a remote host's terminals — the merge deliberately ignores it under a remote host.

### Proposal

The host already knows the answer. `terminal.list` is an existing runtime RPC returning `RuntimeTerminalSummary[]`, and each row carries both `ptyId` and `title` — exactly the mapping needed to name a snapshot session.

- Add an optional `title` to `SessionMemory`. Optional, so an older host that never sets it still decodes.
- After fetching a remote snapshot, enrich its sessions from that host's `terminal.list`, keyed by `ptyId`.
- Prefer the client's own tab title where one exists (unchanged), then the host-reported title, then `pid `.

Two things to be careful about:

- **Cost.** The panel polls every 2s and a second RPC per tick is not free, especially with many terminals. Titles change rarely, so the terminal list should be cached per host with a short TTL and requested without visual layouts (~31% of the payload) or fresh liveness probes.
- **Degradation.** A host that fails or does not answer `terminal.list` must not fail the snapshot. Losing titles should cost the labels only, leaving today's `pid ` behaviour intact.

### Scope

Naming only. This does not make remote rows clickable or killable — navigation still needs a local tab, and kill needs `terminal.stop` routing plus the live/unverifiable/exited verdicts from `docs/reference/ssh-execution-boundary.md`.

Depends on #16000, which introduces the remote snapshot path this would enrich.

Start with resolveSnapshotSessionLabel() in mergeSnapshotAndSessions.ts, SessionMemory in src/shared/process-stats-types.ts, and the existing terminal.list RPC returning RuntimeTerminalSummary[]. Trace the remote snapshot path from #16000 and determine where host terminal titles can be cached and merged. Done means remote sessions prefer local tab titles, then host-reported titles, then pid labels, while terminal.list failures leave snapshots working unchanged.

Written by the indexing model from the issue text.