feat(opencode): Phase 1 - Backend data structure expansion for OpenCode support

Add OpenCode as the 4th supported application with additive provider management:

- Add OpenCode variant to AppType enum with all related match statements
- Add enabled_opencode field to McpApps and SkillApps structures
- Add opencode field to McpRoot and PromptRoot
- Add database schema migration v3→v4 with enabled_opencode columns
- Add settings.rs support for opencode_config_dir and current_provider_opencode
- Create opencode_config.rs module for config file I/O operations
- Update all services (proxy, mcp, skill, provider, stream_check) for OpenCode
- Add OpenCode support to deeplink provider and MCP parsing
- Update commands/config.rs for OpenCode config status and paths

Key design decisions:
- OpenCode uses additive mode (no is_current needed, no proxy support)
- Config path: ~/.config/opencode/opencode.json
- MCP format: stdio→local, sse/http→remote conversion planned
- Stream check returns error (not yet implemented for OpenCode)

src-tauri/src/database/dao/mcp.rs

@@ -13,7 +13,7 @@ impl Database {
     pub fn get_all_mcp_servers(&self) -> Result<IndexMap<String, McpServer>, AppError> {
         let conn = lock_conn!(self.conn);
         let mut stmt = conn.prepare(
-            "SELECT id, name, server_config, description, homepage, docs, tags, enabled_claude, enabled_codex, enabled_gemini
+            "SELECT id, name, server_config, description, homepage, docs, tags, enabled_claude, enabled_codex, enabled_gemini, enabled_opencode
              FROM mcp_servers
              ORDER BY name ASC, id ASC"
         ).map_err(|e| AppError::Database(e.to_string()))?;
@@ -30,6 +30,7 @@ impl Database {
                 let enabled_claude: bool = row.get(7)?;
                 let enabled_codex: bool = row.get(8)?;
                 let enabled_gemini: bool = row.get(9)?;
+                let enabled_opencode: bool = row.get(10)?;
 
                 let server = serde_json::from_str(&server_config_str).unwrap_or_default();
                 let tags = serde_json::from_str(&tags_str).unwrap_or_default();
@@ -44,6 +45,7 @@ impl Database {
                             claude: enabled_claude,
                             codex: enabled_codex,
                             gemini: enabled_gemini,
+                            opencode: enabled_opencode,
                         },
                         description,
                         homepage,
@@ -68,8 +70,8 @@ impl Database {
         conn.execute(
             "INSERT OR REPLACE INTO mcp_servers (
                 id, name, server_config, description, homepage, docs, tags,
-                enabled_claude, enabled_codex, enabled_gemini
-            ) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10)",
+                enabled_claude, enabled_codex, enabled_gemini, enabled_opencode
+            ) VALUES (?1, ?2, ?3, ?4, ?5, ?6, ?7, ?8, ?9, ?10, ?11)",
             params![
                 server.id,
                 server.name,
@@ -84,6 +86,7 @@ impl Database {
                 server.apps.claude,
                 server.apps.codex,
                 server.apps.gemini,
+                server.apps.opencode,
             ],
         )
         .map_err(|e| AppError::Database(e.to_string()))?;