Update README and future-plans to reflect current state

README: add PDF attachments, maintenance menu, mv-sync build step,
resizable pane, URL-based navigation, word-split search, grid highlights.
future-plans: add render_field_value integrations, field types, PDF paging,
inventory/grid URL state; update state variable list.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

README.md

@@ -9,24 +9,49 @@ field values, physical storage locations, and visual panel/grid layouts.
 Define reusable component types (e.g. Resistor, Capacitor, IC) with custom fields per component.
 Components show up in inventory entries and can be navigated to directly from storage locations.
 
+- Word-split search: searching `0603 res` matches `Resistor 0603`
+- Selected component reflected in URL (`/components/:id`) — survives page refresh
+- Resizable list pane (width persisted in localStorage)
+- Duplicate button to quickly clone a component
+- Field values sorted alphabetically, rendered centrally (units, URLs as links, extensible)
+
 ### Fields
-Create custom field definitions (e.g. `resistance`, `capacitance`, `package`) that can be attached
-to any component. Field values are entered per-component instance.
+Create custom field definitions (e.g. `resistance`, `capacitance`, `package`) with an optional
+unit suffix. Unit is appended directly to the value with no space, so you can write `4k7` for a
+resistance field with unit `Ω` and it displays as `4k7Ω`.
+
+URL-like field values (beginning with `http://` or `https://`) are automatically rendered as
+clickable links.
 
 ### Inventory
 Log where things are stored. Each inventory entry links a component to a storage location.
 Supported location types:
 
-- **Grid cell** — a specific row/column in a named grid (e.g. drawer divider box)
+- **Grid cell** — a specific row/column in a named grid (e.g. drawer divider box), picked
+  visually with a graphical cell picker
 - *(plain entries without a grid reference work too)*
 
+Notes on inventory entries are per storage location (not per component).
+
 ### Grids
 Model physical storage grids (drawer organizers, parts boxes, etc.).
 
 1. Upload a photo of the grid
-2. Set up corner points to map the image to a logical grid
+2. Set up corner points to map the image to a logical grid (corners can extend outside image bounds)
 3. Define row/column counts
-4. Click any cell to see what's stored there
+4. Click any cell to see what's stored there — component entries are links, middle-click opens in new tab
+5. Each cell shows a green count badge of how many components reference it
+6. Navigating to a grid from a component detail highlights and scrolls to the relevant cell
+
+### PDF Attachments
+Attach PDF datasheets or other documents to components.
+
+- PDFs are stored with a sanitized human-readable filename derived from the display name
+- Rename a PDF and the file on disk is also renamed, atomically (uses `renameat2 RENAME_NOREPLACE`
+  via `tools/mv-sync`)
+- First-page thumbnails generated automatically via `pdftoppm` (poppler-utils) if available
+- Multiple components can share the same PDF
+- Click any thumbnail to open it full-size in a lightbox
 
 ### Templates (Name Formatters)
 Write JavaScript formatter functions that generate smart display names for components based on their
@@ -48,10 +73,18 @@ Multiple formatters are tried in order.
 The template editor includes a test data box so you can preview the output without needing real
 inventory data.
 
+### Maintenance
+A ⚙ menu in the top-right corner provides maintenance operations:
+
+- **Generate missing PDF thumbnails** — scans all PDFs and generates thumbnails for any that
+  don't have one yet (useful if `pdftoppm` was unavailable at upload time)
+
 ## Requirements
 
 - Node.js >= 25
 - npm
+- `gcc` (to build `tools/mv-sync` — only needed once)
+- `pdftoppm` from poppler-utils (optional, for PDF thumbnails)
 
 ## Install
 
@@ -69,6 +102,15 @@ cd electronics-inventory
 npm install
 ```
 
+## Build native tools
+
+```bash
+cd tools && make
+```
+
+This compiles `mv-sync`, a small helper that performs an atomic rename-without-overwrite using
+`renameat2(RENAME_NOREPLACE)` (Linux 3.15+). It is required for PDF file operations.
+
 ## Run
 
 ```bash
@@ -94,8 +136,9 @@ PORT=8080 BIND_ADDRESS=0.0.0.0 npm start   # both
 
 All data is stored locally in a `data/` directory created automatically on first run:
 
-- `data/db.json` — component, field, inventory, grid, and template records (flat key-value store)
-- `data/uploads/` — source images uploaded for grid setup
+- `data/db.json` — component, field, inventory, grid, template, and PDF records (flat KV store)
+- `data/images/` — uploaded source images and component/inventory photos
+- `data/pdfs/` — uploaded PDF files and their thumbnails
 
 No external database is required.
 
@@ -107,11 +150,17 @@ lib/
   storage.mjs       Server-side KV store wrappers
   kv-store.mjs      JSON file-backed key-value store
   ids.mjs           ID generation
+  grid-image.mjs    Grid image processing helpers
+tools/
+  mv-sync.c         Atomic rename helper (renameat2 RENAME_NOREPLACE)
+  Makefile
 public/
   app.mjs           Single-page app (vanilla JS ES modules)
   templates.html    HTML templates (lazy-loaded)
   style.css         Styles
-  lib/api.mjs       Fetch wrappers for the REST API
+  lib/
+    api.mjs         Fetch wrappers for the REST API
+    dom.mjs         DOM helpers
   views/
     grid-setup.mjs  Canvas-based grid corner editor
 ```