fix: apply cargo clippy fixes across workspace

[devin-ai-integration]

Summary

Mechanical clippy lint fixes applied via cargo clippy --fix and manual edits for warnings that couldn't be auto-fixed. Changes span 11 files across apps/, crates/, and plugins/.

Categories of fixes:

• Collapsed nested if/if let → let-chain expressions (Rust 1.87+ syntax) in validate.rs, entry.rs, extractor.rs, billing.rs, server/mod.rs
• saturating_sub instead of manual arithmetic checks in app.rs
• ? operator instead of let...else { return None } in app.rs
• &Path instead of &PathBuf in function signature (audio_drop.rs)
• Removed needless borrows (&query → query, &env → env)
• !(0..100).contains() instead of manual range check (ext.rs)
• .is_multiple_of() instead of % > 0 (onnx/mod.rs)
• Added Default impl for CallbackServerState (server/mod.rs)
• Workspace fix: added plugins/extensions to exclude list (no Cargo.toml present)

One warning intentionally not fixed: large_enum_variant in crates/template-app/src/lib.rs — boxing the variant would change the serde serialization shape.

Updates since last revision

• Fixed fmt CI failure: rustfmt --edition 2024 formats let-chain opening braces on a new line (different from default rustfmt style). Applied correct formatting to validate.rs and entry.rs.

Review & Testing Checklist for Human

• Spot-check that the collapsed if let chains in crates/tiptap/src/validate.rs (9 occurrences) preserve the original control flow — the nested braces were removed but the error-push logic should be identical
• Confirm plugins/extensions/ genuinely has no Cargo.toml and should be excluded from the workspace (it was deleted from main but the directory glob still matches it)
• Run integration tests for audio file dropping (CLI) to verify the &PathBuf → &Path signature change didn't break anything

Notes

• Changes were only verified on Linux via clippy. macOS-only crates (am2, notch, tcc, notification-macos, audio, audio-device, bundle, detect, device-monitor, email, intercept, mac, vad-ext, cactus) were excluded from the clippy run due to platform-specific dependencies.
• No behavioral changes intended — all fixes are code style/idiom improvements flagged by clippy.

Requested by: bot_apk
Devin Session

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR that start with 'DevinAI' or '@devin'.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring

[netlify]

✅ Deploy Preview for hyprnote canceled.

Name	Link
🔨 Latest commit	1973454
🔍 Latest deploy log	https://app.netlify.com/projects/hyprnote/deploys/69a4ddf73553e50008fe2497

[netlify]

✅ Deploy Preview for hyprnote-storybook canceled.

Name	Link
🔨 Latest commit	1973454
🔍 Latest deploy log	https://app.netlify.com/projects/hyprnote-storybook/deploys/69a4ddf778186200080060eb