emrg: bump version to v0.2.50 (release: #847)

[argszero]

Release v0.2.50 (host instruction 2026-08-18).

Covers the 1 commit since v0.2.49 — PR #847 (two fixes):

• stop_all self-held lock attribution: python-dist locks held only by stop_all's own process (interpreter DLLs, released on exit) are no longer treated as residual blockers — external-process locks still get killed + abort; last piece of the Windows installer DeleteFile code 5 chain (v0.2.49 field evidence: killed browser-harness but was blocked by 12 self python-dist locks misjudged as RESIDUAL)
• TUI user messages render via Markdown widget (Plan B): reuses the assistant rich_renderable_to_lines pipeline — wraps by width natively (fixes long-line loss after multi-line send), supports markdown styling, keeps the '> ' cyan prefix

Bump: 8 files / 9 places 0.2.49 → 0.2.50 (same pattern as prior releases):

• emrg/init.py, pyproject.toml, emrg/gui/package.json + package-lock.json (2), packaging/build-runtime.sh, packaging/make-installer.sh, packaging/make-run-installer.sh, uv.lock

Verification: pytest 961 passed + 1 skipped, import OK, CLI OK, version-sync + doc-count guards green.

[argszero]

✅ LGTM — cycle 755. Diff verified: 8 files / 9 places 0.2.49 → 0.2.50 (emrg/init.py, pyproject.toml, gui/package.json + package-lock.json ×2, build-runtime.sh, make-installer.sh, make-run-installer.sh, uv.lock). CI: test + test-windows PASS (run 32135359264). Local: pytest 961 passed + 1 skipped, version-sync + doc-count guards green.

[argszero]

✅ LGTM — cycle 756. Independent re-review: head unchanged (e152dcf), CI test + test-windows PASS (run 32135359264), mergeable. Bump diff = 8 files / 9 places 0.2.49 → 0.2.50 exactly per host release spec.

[argszero]

✅ LGTM — cycle 757 (3rd). Head e152dcf unchanged, CI test + test-windows PASS (run 32135359264), mergeable. Bump verified against host release spec (8 files / 9 places 0.2.49 → 0.2.50). 3 consecutive LGTMs from cycles 755/756/757 — merging.