chore(desktop): clear desktop-tauri clippy backlog

[wesbillman]

Summary

Clears all 26 pre-existing clippy -D warnings errors in the desktop Tauri crate so just desktop-tauri-clippy — and with it the local just check aggregate — passes again. CI doesn't run this target, so the backlog had accumulated on main (flagged during #1601/#1602 review as a separate cleanup chunk).

No behavior change intended anywhere in this diff.

What was fixed, by category

Mechanical simplifications (bulk):

• readiness.rs: map_or → is_none_or/is_some_and; collapsed if-into-match-guard on the provider credential matches (semantics verified: a present key fails the guard and falls through to the empty _ arm, identical to the old inner-if-does-nothing)
• runtime.rs: removed unused pub use sweep::{...} re-export (all uses are inside sweep.rs), iter().any() → slice::contains
• archive/mod_tests.rs: 4× needless borrow on "A".repeat(200)
• personas/writeback.rs: redundant closure
• config_bridge/claude.rs test helper: struct-literal init instead of field-reassign-with-default

Root-cause fixes rather than lint silencing:

• agent_models.rs: the identical if blocks lint exposed that preserve_first_separator was inert (both arms returned part at index 0) — removed the parameter entirely
• config_bridge/reader.rs: named ResolvedOverride type alias for the very-complex-type lint

Deliberate #[allow]s with rationale comments:

• too_many_arguments ×4 (archive/store.rs ×2, archive/pipeline.rs, config_bridge/reader.rs): these fns mirror table columns or are single-caller internals — a params struct would rename the problem, not fix it
• readiness.rs config_file_path dead-code: kept behind #[allow(dead_code)] + note because the in-flight unified-agent-record work (chunk A) replaces that resolution path wholesale; deleting it here would create churn against that branch
• readiness.rs is_ready/requirements: used only by tests → gated #[cfg(test)]; Requirement::label() had zero callers → deleted

Coordination note

runtime.rs/readiness.rs changes were kept intentionally mechanical to avoid conflicting with the in-flight feat/unified-agent-record branch, per agreement with its author.

Testing

• just desktop-tauri-clippy green (was 26 errors)
• just desktop-tauri-fmt-check green
• file-size gate green
• 1023 desktop Rust tests pass