feat: add evidence search and stabilize pdf previews

- add document evidence parsing/search/open routes, Hermes tool wiring, local index settings/status, and the document-evidence skill plus design notes
- fix PDF resource tabs by rendering PDFs inline with pdf.js canvases instead of iframe preview pages, release PDF documents on close, and document the fourth-PDF stall bug
- keep PDF preview at 2x rendering while removing the previous lazy-load/placeholder direction, and make dev:hot bind loopback defaults externally reachable

Verification:
- node --check rust/crates/mnote-web/browser/document-resource-tab-runtime.js
- node scripts/task-dev-hot-plan-test.js
- cargo test -p mnote-web --manifest-path rust/Cargo.toml pdf_preview_page_does_not_render_visible_toolbar
- cargo test -p mnote-web --manifest-path rust/Cargo.toml document_shell_returns_page_aggregate_snapshot
- cargo build -p mnote-web --manifest-path rust/Cargo.toml
- browser smoke: sequentially opened the four tea_seed_oil_cosmetic PDFs; fourth PDF rendered 15/15 canvases, iframeCount=0, browser errors=0

rust/crates/mnote-web/Cargo.toml

@@ -17,6 +17,7 @@ hyper-util = { version = "0.1", features = ["tokio"] }
 leptos = { version = "0.8.14", default-features = false, features = ["ssr"] }
 mnote-editor-core = { path = "../mnote-editor-core" }
 reqwest = { version = "0.12", default-features = false, features = ["blocking", "json", "rustls-tls", "stream"] }
+rusqlite = { version = "0.34", features = ["bundled"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 tokio = { version = "1", features = ["macros", "rt-multi-thread", "net", "signal", "sync", "time", "process", "io-util"] }