docs: add a Features section to the README

Document the supported content types (text, URLs, colors, images, files),
full-history FTS search, automatic light/dark theming, lazy loading, dedup,
reliability and privacy behavior, and the panel controls.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

README.md

@@ -6,6 +6,72 @@ All heavy work (hashing, decoding, storage, search, thumbnails) lives in a Rust
 daemon. The GNOME Shell extension only renders UI and forwards events over
 D-Bus, so the compositor is never blocked, even with thousands of items.
 
+## Features
+
+**Content types.** Strata captures and previews:
+
+- **Text** (UTF-8). When an app offers both rich and plain text, Strata stores
+  the plain text rather than styled HTML.
+- **URLs** are shown link-styled, with the hostname as a subtitle.
+- **Colors**: hex values (`#rgb` / `#rrggbb`) get a color swatch.
+- **Images**: PNG, JPEG, GIF, WebP, BMP, TIFF, ICO, shown as thumbnails.
+  Decoding and resizing happen once, in the daemon, at copy time.
+- **Files**: file-manager copy/cut (URI lists, e.g. from Nautilus).
+
+Unknown MIME types are ignored (a strict allowlist).
+
+**Search.**
+
+- Full-text search over the entire stored history, backed by SQLite FTS5.
+- Prefix matching, diacritic-insensitive (`cafe` matches `café`).
+- Text only; images and binaries are not indexed.
+
+**Appearance.**
+
+- Automatic light/dark theme: `Auto` follows the system color scheme; `Light`
+  and `Dark` force one.
+- Configurable panel position (top/center/bottom by left/center/right), width,
+  and maximum height.
+- Optional "move an item to the top" when you paste it.
+
+**Performance.**
+
+- All hashing, decoding, storage, search, and thumbnailing run in the Rust
+  daemon, off the compositor's main loop.
+- Lazy loading: the panel loads one page of history at a time and fetches more
+  on scroll; thumbnails are fetched on demand and cached on disk; search
+  renders a page at a time. The full table never sits in memory.
+- Deduplication: copying the same content twice moves the existing entry to the
+  top (blake3 content hash) instead of adding a duplicate.
+
+**Reliability.**
+
+- SQLite in WAL mode with atomic upserts; history survives a crash.
+- The extension supervises the daemon, respawning it with exponential backoff.
+  Only one daemon runs at a time; a second exits rather than contend for the
+  bus name.
+- Configurable history limit (default 200, up to 2000); oldest items are pruned
+  automatically.
+
+**Privacy and safety.**
+
+- Password-manager aware: entries marked sensitive (the
+  `x-kde-passwordManagerHint` used by KeePassXC and others) are never stored.
+- App exclusions: items copied while a listed app has focus are skipped. The
+  default list covers common password managers (1Password, KeePassXC,
+  Bitwarden, and others).
+- Size caps: text and image payloads larger than a configurable limit (1 MB and
+  5 MB by default) are not stored.
+- Never executes clipboard content: no shell exec, no `launch_uri`, no markup
+  parsing; paste-back only writes to the clipboard.
+
+**Controls.**
+
+- Top-bar icon and popup panel, opened with a configurable shortcut (default
+  `Super+Shift+V`).
+- Keyboard navigation (arrow keys, `Esc` to close), click-outside to dismiss,
+  per-row delete, and "Clear all".
+
 ## Architecture
 
 Strata is **two components**, and you need **both** for it to work:
@@ -28,7 +94,7 @@ GNOME Shell (GJS)  ──D-Bus──▶  strata-daemon  ──▶  SQLite (~/.lo
 
 ## Requirements
 
-- GNOME Shell 50 (tested). May work on 45–49 but untested — if you try it and it works, please open an issue to let us know.
+- GNOME Shell 50 (tested). May work on 45-49 but is untested; if it works for you, please open an issue to let us know.
 - `strata-daemon` binary in `$PATH` (see Install below)
 - Rust 1.74+ (build only)
 - `glib-compile-schemas` (from `glib2-devel` / `libglib2.0-dev-bin`)