Roadmap (v2.1.0): archive browser-bridge, native-host helper, and launchd runtime modes

[jmcte]

Context

docs/NATIVE_ONLY_REDESIGN.md lines 278-282 list code paths to archive after the cutover:

Code to archive after cutover

• browser-bridge/
• native-host private-helper bridge code
• helper manifest install scripts
• launchd/direct helper runtime modes

These are still in-tree as of v2.0.0 to preserve the v1.x parity line during migration. Once the deprecated commands are removed (companion roadmap issue), the supporting infrastructure should follow.

Scope

• Move browser-bridge/, the private-helper portions of native-host/, helper manifest install scripts, and launchd/direct helper runtime modes out of rust/src/ into the archive.
• Follow docs/ARCHIVE_POLICY.md — preserve under legacy/ rather than deleting outright, so historical comparisons remain reproducible.
• Trim Cargo.toml features and CI matrix entries that exist solely for these paths.

Acceptance criteria

• Active source tree no longer contains the listed paths outside legacy/.
• cargo build and cargo test still pass after the move.
• docs/NATIVE_ONLY_REDESIGN.md "Code to archive after cutover" section is closed out (either removed or marked Done).
• Threat-model refresh issue triggered (separate roadmap item).

[jmcte]

Material PR submitted: #80

Current status:

• The PR archives the browser bridge, native host bundle, helper scripts, and legacy runtime internals under legacy/.
• It removes the active apw host CLI surface and trims the active legacy parity gates.
• CI is green on the PR.

Closure note:

• The PR body contains Closes #47, but it is intentionally stacked on Remove legacy daemon CLI commands #74 because the archive step depends on legacy daemon command removal.
• GitHub will not show this issue as auto-closing while the PR targets another feature branch; after Remove legacy daemon CLI commands #74 lands, Archive legacy runtime internals #80 should be retargeted/merged to main so Roadmap (v2.1.0): archive browser-bridge, native-host helper, and launchd runtime modes #47 closes normally.