cursor + hermes: pre-tool-use can't read /index.md (only intercepts grep/rg, not cat)

## Severity
Medium — feature parity gap with CC + Codex. After commit 4e956fa the virtual /index.md is bounded to 50 most-recently-updated rows with a clean markdown table — exactly the right entry point for "what's recent" queries. CC and Codex both read it. Cursor and Hermes can't.

## Where
- `src/hooks/cursor/pre-tool-use.ts` — only intercepts `grep`/`rg`/`egrep`/`fgrep` shell commands (per the file's docstring)
- `src/hooks/hermes/pre-tool-use.ts` — only intercepts `terminal` events (similar scope)

Compare with `src/hooks/pre-tool-use.ts:107-117` and `:355-380` (CC) where the Read tool + bash `cat`/`head`/`tail` routes through `readVirtualPathContents` — including the special `/index.md` virtual fallback.

## Repro
Inside a Cursor or Hermes session, ask the agent to read the index:

```
cat /.deeplake/memory/index.md
```

The bash command falls through the agent's pre-tool-use hook (only grep is intercepted), then errors with ENOENT against the real filesystem (the path doesn't exist as a real directory). Both agents' SessionStart prompts say "index.md (start here)" but the agents can't actually do it.

## Proposed fix
Port the index.md / direct-read intercept from CC's pre-tool-use:

1. Recognize `cat` / `head` / `tail` / `wc` / Read-tool calls targeting paths under the memory mount.
2. Resolve the read via `readVirtualPathContents` (already imported in CC's hook; just import it in cursor + hermes).
3. Special-case `/index.md` to fall through to the synthesized virtual index (already handled in `readVirtualPathContents`).

Cursor uses `updated_input: { command: 'echo ' }` for grep; for Read it would use the same pattern with content-as-string.

Hermes uses `{action: "block", message: ""}` per the existing pattern.

## Acceptance
- Cursor session: `cat /.deeplake/memory/index.md` returns the bounded markdown table.
- Hermes session: same.
- Existing grep/rg interception unchanged.

## Out of scope
- Pi extension — in-process architecture, separate code path. Tracked in #85 (OpenClaw parity issue).

Found during embedding_generation branch validation, see commit 4e956fa.