feat: add image hash-based OCR caching with 100MB size limit

- Implement SHA-256 image hashing to cache OCR results and avoid re-processing identical images
- Add 100MB file size limit for image uploads with user-friendly error messages
- Clear ghost suggestions when uploading new images to prevent interference
- Optimize size limit calculation in copilot plugin to include OCR context
- Remove debug logging from production code
- Add image processing optimization plan document

BREAKING CHANGE: Image upload size limit is now enforced at 100MB (previously unlimited)

src/utils/api.js

@@ -1,7 +1,6 @@
-import { DEBUG, API_URL } from './config.js'
+import { API_URL } from './config.js'
 
 export async function fetchSuggestion(prefix, suffix, signal, apiUrl = API_URL) {
-    if (DEBUG) console.log('[Debug] fetchSuggestion called with prefix length:', prefix.length, 'suffix length:', suffix.length)
     try {
         const res = await fetch(apiUrl, {
             method: 'POST',
@@ -10,7 +9,6 @@ export async function fetchSuggestion(prefix, suffix, signal, apiUrl = API_URL)
             signal
         })
 
-        if (DEBUG) console.log('[Debug] fetchSuggestion response status:', res.status)
         if (!res.ok) {
             const errorText = await res.text()
             throw new Error(`HTTP ${res.status}: ${errorText}`)
@@ -18,7 +16,6 @@ export async function fetchSuggestion(prefix, suffix, signal, apiUrl = API_URL)
 
         const reader = res.body?.getReader()
         if (!reader) {
-            if (DEBUG) console.log('[Debug] No reader available')
             throw new Error('No reader available')
         }
 
@@ -40,23 +37,20 @@ export async function fetchSuggestion(prefix, suffix, signal, apiUrl = API_URL)
                     const data = JSON.parse(jsonStr)
                     if (data.content) {
                         text += data.content
-                        if (DEBUG) console.log('[Debug] Added content:', data.content)
                     }
                     if (data.done || data.error) break
                 } catch (e) {
-                    if (DEBUG) console.warn('[Debug] JSON parse error for:', jsonStr.substring(0, 50))
+                    // skip invalid lines
                 }
             }
         }
         
-        if (DEBUG) console.log('[Debug] Final suggestion text:', text.substring(0, 100))
         return text
     } catch (e) {
         if (e.name === 'AbortError') {
-            if (DEBUG) console.log('[Debug] Request aborted')
+            // ignore abort
         } else {
-            if (DEBUG) console.error('[Debug] fetchSuggestion error:', e)
+            throw e
         }
-        throw e
     }
 }