feat: switch from OpenAI API to native Ollama Python client

This commit refactors the LLM integration to use Ollama's native Python client instead of OpenAI-compatible API, while fixing critical template syntax errors and improving project structure.

Key changes:
- Replace openai package with ollama package in backend requirements
- Rewrite llm.py to use ollama.AsyncClient for direct Ollama API calls
- Update main.py to use non-streaming Ollama responses with thinking extraction
- Fix template syntax error in MilkdownEditor.vue (GhostTextOverlay component tags)
- Fix string截取错误 by using slice() instead of substring()
- Add src/utils/api.js and src/utils/config.js for shared configuration
- Add CORS middleware to FastAPI backend
- Update prompt.py with clearer instructions for continuation generation
- Add comprehensive README.md documentation

BREAKING CHANGE: Environment variables OLLAMA_BASE_URL changed to OLLAMA_HOST (remove /v1/ suffix)

src/utils/api.js

@@ -0,0 +1,52 @@
+import { DEBUG, API_URL } from './config.js'
+
+export async function fetchSuggestion(prefix, suffix, 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',
+            headers: { 'Content-Type': 'application/json' },
+            body: JSON.stringify({ prefix, suffix, languageId: 'markdown' }),
+        })
+
+        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}`)
+        }
+
+        const reader = res.body?.getReader()
+        if (!reader) {
+            if (DEBUG) console.log('[Debug] No reader available')
+            throw new Error('No reader available')
+        }
+
+        let text = ''
+        while (true) {
+            const { done, value } = await reader.read()
+            if (done) break
+            const chunk = new TextDecoder().decode(value)
+            if (DEBUG) console.log('[Debug] Received chunk:', chunk.substring(0, 100))
+            
+            const lines = chunk.split('\n').filter(l => l.startsWith('data: '))
+            for (const line of lines) {
+                try {
+                    const data = JSON.parse(line.slice(6))
+                    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:', e)
+                }
+            }
+        }
+        
+        if (DEBUG) console.log('[Debug] Final suggestion text:', text.substring(0, 100))
+        return text
+    } catch (e) {
+        if (DEBUG) console.error('[Debug] fetchSuggestion error:', e)
+        throw e
+    }
+}