Review and merge PR #100 for release/v0.2.53

[pranavp311]

Owner review request for PR #100: #100

PR #100 adds the macOS-first mer native shell for release/v0.2.53: WebView shell, manifest-driven packaging, and window.mer.invoke bridge.

Readiness work completed on the PR branch:

• Fixed native CLI/scaffold merge blockers: mer add native now emits native, native-build, and package steps; mer native propagates failed child exits; package output uses the manifest display name.
• Hardened the bridge: manifest allowed origins are parsed and enforced before dispatch; payload/origin errors resolve the original Promise id.
• Added macOS app lifecycle handling so closing the last window terminates the app.
• Updated native docs/plan/manifest to v0.2.53 and enabled CI for release/** PR targets.

Local verification passed:

• zig build test
• zig build cli
• zig build desktop
• zig build native-build -Doptimize=ReleaseSmall
• zig build package -Doptimize=ReleaseSmall
• git diff --check

Requested owner actions:

• Review PR feat(native): mer native — WebView shell + window.mer.invoke bridge (P0–P3) #100.
• Let release-targeted CI run after the latest push.
• Merge PR feat(native): mer native — WebView shell + window.mer.invoke bridge (P0–P3) #100 into release/v0.2.53 if acceptable.

This issue can be closed when PR #100 is merged.