emrg: escape PowerShell braces in stop_tui ps_cmd (Windows emrg stop crash)

[pm25coder]

Fix a Windows runtime crash in emrg stop introduced by the #811 merge: emrg/_stop_all.py stop_tui() builds its PowerShell CIM query with str.format(own=own) but the template contains literal PowerShell script-block braces (Where-Object { ... } / ForEach-Object { ... }). str.format() parses those as replacement fields and raises ValueError: unexpected '{' in field name on every Windows run of emrg stop — before stop_bundled_git() and verify() ever execute, so the installer's bundled-git orphan cleanup (#683/#689/#692 family) never runs.

Why CI missed it: tests/test_stop_all.py monkeypatches stop_tui entirely (orchestration tests), and test_installer_stop.py only does textual wiring asserts — the template is never rendered anywhere in the test suite. This regressed on Windows immediately after the merge.

Changes:

• emrg/_stop_all.py — escape the literal braces as {{ }} in the stop_tui() ps_cmd template, keeping {own} as the only real replacement field. Verified the rendered PowerShell is byte-identical to the intended command (e.g. Where-Object { $_.ProcessId -ne 12345 ... }).
• tests/test_stop_all.py — new TestStopTuiPsTemplate::test_stop_tui_renders_ps_template_win: forces the Windows branch (is_win → True), monkeypatches subprocess.run to capture the command, calls stop_tui(), and asserts (a) no ValueError is raised, (b) the invoking-PID exclusion is substituted, (c) the literal Where-Object { / ForEach-Object { blocks survive. This pins the render path so a regression is caught at the unit level. (Discriminative: the unfixed template raises ValueError at the .format() line.)
• Agent.md — Python test count 858 → 859 (doc-count guard).

Verified: uv run pytest tests/ -v → 859 collected (799 passed + 60 skipped) green; import + python -m emrg --help OK.

[argszero]

✅ LGTM — cycle (review): genuine bug caught — my #811's stop_tui() used str.format(own=own) on a template containing literal PowerShell { } script-block braces, which raises ValueError: unexpected '{' in field name on every Windows emrg stop run before stop_bundled_git/verify execute. Verified the discriminator both ways: master's template raises ValueError, the escaped {{ }} template renders correctly with the PID exclusion substituted. The new unit test forces the Windows branch and pins the render path (positive + negative states). Merge conflict resolved by author (Agent.md 869). CI test + test-windows PASS.