feat(hashline): port hashline edit tool from oh-my-pi

This PR ports the hashline edit tool from oh-my-pi to oh-my-opencode as an experimental feature.

## Features
- New experimental.hashline_edit config flag
- hashline_edit tool with 4 operations: set_line, replace_lines, insert_after, replace
- Hash-based line anchors for safe concurrent editing
- Edit tool disabler for non-OpenAI providers
- Read output enhancer with LINE:HASH prefixes
- Provider state tracking module

## Technical Details
- xxHash32-based 2-char hex hashes
- Bottom-up edit application to prevent index shifting
- OpenAI provider exemption (uses native apply_patch)
- 90 tests covering all operations and edge cases
- All files under 200 LOC limit

## Files Added/Modified
- src/tools/hashline-edit/ (7 files, ~400 LOC)
- src/hooks/hashline-edit-disabler/ (4 files, ~200 LOC)
- src/hooks/hashline-read-enhancer/ (3 files, ~400 LOC)
- src/features/hashline-provider-state.ts (13 LOC)
- src/config/schema/experimental.ts (hashline_edit flag)
- src/config/schema/hooks.ts (2 new hook names)
- src/plugin/tool-registry.ts (conditional registration)
- src/plugin/chat-params.ts (provider state tracking)
- src/tools/index.ts (export)
- src/hooks/index.ts (exports)

src/plugin/tool-registry.ts

@@ -25,6 +25,7 @@ import {
   createTaskGetTool,
   createTaskList,
   createTaskUpdateTool,
+  createHashlineEditTool,
 } from "../tools"
 import { getMainSessionID } from "../features/claude-code-session-state"
 import { filterDisabledTools } from "../shared/disabled-tools"
@@ -117,6 +118,11 @@ export function createToolRegistry(args: {
       }
     : {}
 
+  const hashlineEnabled = pluginConfig.experimental?.hashline_edit ?? false
+  const hashlineToolsRecord: Record<string, ToolDefinition> = hashlineEnabled
+    ? { hashline_edit: createHashlineEditTool() }
+    : {}
+
   const allTools: Record<string, ToolDefinition> = {
     ...builtinTools,
     ...createGrepTools(ctx),
@@ -132,6 +138,7 @@ export function createToolRegistry(args: {
     slashcommand: slashcommandTool,
     interactive_bash,
     ...taskToolsRecord,
+    ...hashlineToolsRecord,
   }
 
   const filteredTools = filterDisabledTools(allTools, pluginConfig.disabled_tools)