Add batch reads, @file completion, interruptible commands, tool sets

Tools, six built-in to fourteen:
- read_many_files: up to 20 paths read concurrently, each with its own window.
  An unreadable path is reported in its own block instead of throwing.
- multi_edit: several edits to one file, validated in memory first so a late
  failure cannot leave the file half-written.
- list_dir: ignore-aware depth-limited tree.
- git_status/diff/log/show/blame: read-only, spawned with a fixed argv rather
  than a shell string, which is what makes them safe to auto-approve.

toolSets gates them. core is always on; edit-plus and git are optional. A
disabled set reaches neither the wire nor the system prompt, since a prompt
naming an absent tool teaches calls that cannot succeed.

Interface:
- Reasoning streams to a collapsed panel, ctrl-r expands, dropped when the turn
  ends: it is progress, not the answer.
- The tool in flight is named from tool-input-start, before its arguments finish
  streaming, and cleared on its result.
- Prompts typed mid-turn queue and drain in order. esc clears the queue as well
  as aborting.
- @ opens a path picker fed by the ignore-aware walker. Prefix matches rank
  above substring matches, so @src/ means "under src/". The walk runs on the
  first @, not at startup.

ctrl-c kills the command in flight and keeps the turn. The call throws rather
than returning, so the model cannot read a killed command as one that ran and
failed on its own terms. The kill takes the whole process tree: killing cmd /c
alone left the real command holding both pipes open, so the read never returned
and the interrupt did nothing for 19 seconds.

Two pruning fixes:
- A tool result whose tool call was pruned is now dropped with it. Pruning
  counts messages, so the cut landed between an assistant tool-call and the tool
  message answering it, producing 400 "No tool call found for function call
  output with call_id ...". The reverse pairing is left alone: a call awaiting
  its result is what a suspended approval looks like.
- ignore.ts called statFs without importing it, so walk() crashed on the first
  symlink.

482 tests, up from 404. Docs synced across README, ROADMAP, TODO, and all of
docs/: tool sets, the new tools, ctrl-c semantics, the tool-start event, and the
two hand-maintained tool-name lists recorded as a known weakness.

docs/configuration.md

@@ -21,6 +21,7 @@ Written by `/provider`, editable by hand. Every field is optional.
   "thinking": "medium",
   "maxRetries": 3,
   "plugins": ["guard", "time"],
+  "toolSets": ["edit-plus", "git"],
   "mcpServers": {
     "fs": { "command": "npx", "args": ["-y", "@modelcontextprotocol/server-filesystem", "."] }
   }
@@ -38,6 +39,7 @@ Written by `/provider`, editable by hand. Every field is optional.
 | `thinking` | default level: `off`, `low`, `medium`, `high`, `max` |
 | `maxRetries` | retries per model call for transient failures. Default 3 |
 | `plugins` | which plugins to enable. Omit for `["guard", "time"]` |
+| `toolSets` | optional tool sets beyond `core`: `edit-plus`, `git`. Omit for all of them. See [tools](tools.md) |
 | `mcpServers` | see [MCP](mcp.md) |
 
 ## Provider presets