feat: OCR a camera shot / image into the input via Tesseract.js

New "Scan image" button in the input pane header:

- Opens the phone's rear camera (capture=environment) or a desktop
  file picker via a hidden <input type="file">.
- On image selected, lazy-imports tesseract.js from esm.sh — no
  bundling, no Docker image growth.
- Language follows the "From" dropdown (ISO 639-2 mapping for the
  30 currently-supported languages). "Auto-detect" loads the
  eng+por+deu+nld pack and lets tesseract pick.
- Progress status renders below the input (engine load → OCR
  percentage → "done in Xs").
- Result replaces the editor contents; existing vim bindings,
  Shift-H/L nav, Ctrl-Enter translate all keep working.

First scan triggers a ~5 MB Tesseract WASM download plus the chosen
language pack (~3-10 MB). Cached by the browser after.

CHANGELOG.md

@@ -7,6 +7,9 @@ Versioning: [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
 
+### Added
+- "Scan image" button next to the input pane: opens the phone's rear camera (or a file picker on desktop), runs OCR locally in the browser via Tesseract.js (loaded from esm.sh on first use), and replaces the editor contents with the recognised text. Language follows the "From" dropdown via an ISO 639-2 mapping; "Auto-detect" loads a common European set (`eng+por+deu+nld`). Progress status shows beneath the input ("Loading OCR engine…" → "OCR 40%" → "OCR done in 3.2s"). Zero image-size cost — same CDN pattern as CodeMirror.
+
 ## [0.2.0] - 2026-06-09
 
 ### Added