feat(state): add scoped slice persistence

[cooper (czxtm)]

Summary

Test Plan

Docs

• Docs updated (companion PR in darkmatter/nixmac-web: #___)
• No docs update needed

[cooper (czxtm)]

Warning

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• refactor(frontend): move backend mirrors to viewmodel #255
• chore(beads): update state migration issues #254
• chore(fmt): add treefmt wiring #253
• feat(console): add resizable log panel #252
• fix(theme): scope Minted to Monaco diffs #251
• feat(settings): split backup and tuning panels #250
• chore(credentials): remove legacy plaintext fallback #249
• feat(state): wire runtime slices and summarizer #248
• feat(db): add Diesel pool and table models #247
• feat(state): add scoped slice persistence #246 👈 (View in Graphite)
• refactor(configurable): split derive and generated UI #245
• docs(state): add migration plan issues #244
• implement derive(Configurable) macro #228 : 1 other dependent PR (#229 )
• develop

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[github-actions]

	Warnings
⚠️	Your ## Test Plan section is empty. Describe the steps a reviewer should take to verify this change.
⚠️	❗ Big PR (1630 lines changed). Consider splitting it into smaller, focused changes.
⚠️	New Rust modules were added without tests. Consider adding a #[cfg(test)] mod tests { ... } block or a file under apps/native/src-tauri/tests/: apps/native/src-tauri/src/state/slice/json_io.rs apps/native/src-tauri/src/state/slice/registry.rs
⚠️	This PR touches behavior-sensitive code that is documented in darkmatter/nixmac-web. Please either: Open a companion docs PR and check Docs updated in the PR description, or Check No docs update needed if the change doesn't affect user-facing behavior.

📋 PR Overview

Lines changed	1630 (+1531 / -99)
Files	8 added, 10 modified, 0 deleted
Draft / WIP	no
Has Test Plan	yes
New UI components	no
New Storybook stories	no
New Rust modules	yes (8)
New TS source files	no
New tests	no
package.json touched	no
Cargo.toml touched	no
Infra / CI touched	no

🔬 Coverage

Report	Lines	Statements	Functions	Branches
apps/native/coverage/coverage-summary.json	17.6%	17.6%	31.0%	54.1%

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