feat: stamp build identity into every target

[Alex Shabalin (alex-sparus)]

Summary

Problem: helper upgrades hinge on exact build identity — activation is admitted only between binaries of the same build, and a GUI whose bundle was replaced underneath it must notice and stop mutating — but no binary or bundle could say which build it came from, and nothing distinguished a canonical /Applications install from a displaced copy.

Solution: one NIXMAC_BUILD_ID resolution in build.rs feeds both the compiled constant in every target and the stamped Info.plist (now generated from a template), so running-vs-on-disk comparison is possible. Packaged builds fail without a CI-supplied ID; dev builds fall back to a fixed literal. install_location supplies the canonical-install verdict the later gates consume.

First PR of the helper-redesign stack (#667 → #668 → #669 → #670).

Test Plan

• cargo test green across all targets (build-ID resolution and install-location judgment covered by unit tests)
• CI gains a macOS cargo test -p nixmac job so the cfg(macos) helper coverage actually executes

Docs

• No docs update needed

Prior review

Every file in this PR is byte-identical to content Scott already approved in the closed drain-era stack: build.rs/build_id.rs/Cargo plumbing in #619 and #620, install_location.rs in #635, Info.template.plist/tauri.conf.json/settings in #620. This PR is a re-cut of that reviewed work onto the new stack; nothing changed but the commit story.

[Alex Shabalin (alex-sparus)]

• feat(ui): surface helper state and actions feat(ui): surface helper state and actions #670
• feat(helper): reconcile installs, route applies feat(helper): reconcile installs, route applies #669
• feat(helper)!: detach activations, freeze wire feat(helper)!: detach activations, freeze wire #668
• feat: stamp build identity into every target feat: stamp build identity into every target #667 👈
• refactor(helper): drop stderr from response refactor(helper): drop stderr from response #616
• fix(helper)!: drop claimed identity, version the protocol fix(helper)!: drop claimed identity, version the protocol #615
• fix(helper): validate socket peers by code signature fix(helper): validate socket peers by code signature #597
• main

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This stack of pull requests is managed by jj-ryu.

[darkmatter]

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These stories' HTML snapshots changed. I've added screenshots + links to the changed stories below. Review them carefully then accept the changes to regenerate baselines and include them in this PR:

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Flows/Evolve › 2. Evolving (progress)

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[github-actions]

	Warnings
⚠️	No Linear issue ID found in this PR's title, description, or branch name (expected something like ENG-123). Add one so this work is traceable in Linear, or add #no-linear to the PR description to acknowledge it's intentionally untracked.
⚠️	PR is marked WIP / draft — do not merge until ready for review.

	Messages
📖	🤖 This PR touches CI / infra — reviewers please pay extra attention: .github/workflows/build.yaml

📋 PR Overview

Lines changed	626 (+589 / -37)
Files	1 added, 6 modified, 0 deleted
Draft / WIP	yes
Has Test Plan	yes
Linear issue	no
No Test Plan Needed	no
New UI components	no
New Storybook stories	no
New Rust modules	yes (1)
New TS source files	no
New tests	no
package.json touched	no
Cargo.toml touched	no
Infra / CI touched	yes

🔬 Coverage

Report	Lines	Statements	Functions	Branches
apps/native/coverage/coverage-summary.json	35.6%	35.2%	30.5%	29.5%

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