docs: #155 — add USAGE.md documentation for /ultraplan, /teleport, /bughunter commands

## Problem

Three interactive slash commands are documented in `claw --help` but have no
corresponding section in USAGE.md:

- `/ultraplan [task]` — Run a deep planning prompt with multi-step reasoning
- `/teleport <symbol-or-path>` — Jump to a file or symbol by searching the workspace
- `/bughunter [scope]` — Inspect the codebase for likely bugs

New users see these commands in the help output but don't know:
- What each command does
- How to use it
- When to use it vs. other commands
- What kind of results to expect

## Fix

Added new section "Advanced slash commands (Interactive REPL only)" to USAGE.md
with documentation for all three commands:

1. **`/ultraplan`** — multi-step reasoning for complex tasks
   - Example: `/ultraplan refactor the auth module to use async/await`
   - Output: structured plan with numbered steps and reasoning

2. **`/teleport`** — navigate to a file or symbol
   - Example: `/teleport UserService`, `/teleport src/auth.rs`
   - Output: file content with the requested symbol highlighted

3. **`/bughunter`** — scan for likely bugs
   - Example: `/bughunter src/handlers`, `/bughunter` (all)
   - Output: list of suspicious patterns with explanations

## Impact

Users can now discover these commands and understand when to use them without
having to guess or search external sources. Bridges the gap between `--help`
output and full documentation.

Also filed ROADMAP #155 documenting the gap.

Closes ROADMAP #155.

ROADMAP.md

@@ -5960,3 +5960,42 @@ But USAGE.md documents that "The error message now includes a hint that names th
 **Blocker:** None. Pure error-message UX improvement.
 
 **Source:** Clawhip nudge 2026-04-21 21:37 KST — discovered during dogfood probing of model validation.
+
+## Pinpoint #155. USAGE.md missing docs for `/ultraplan`, `/teleport`, `/bughunter` commands
+
+**Gap.** The `claw --help` output lists three interactive slash commands that are not documented in USAGE.md:
+- `/ultraplan [task]` — Run a deep planning prompt with multi-step reasoning
+- `/teleport <symbol-or-path>` — Jump to a file or symbol by searching the workspace
+- `/bughunter [scope]` — Inspect the codebase for likely bugs
+
+New users see these commands in the help output but have no explanation of:
+1. What each does
+2. How to use it
+3. What kind of input it expects
+4. When to use it (vs. other commands)
+5. Any limitations or prerequisites
+
+**Impact.** Users run `/ultraplan` or `/teleport` out of curiosity, or they skip these commands because they don't understand them. Documentation should lower the barrier to discovery.
+
+**Fix shape (~100 lines).** Add a new section to USAGE.md after "Interactive slash commands" covering:
+1. **Planning & Reasoning** — `/ultraplan [task]`
+   - Purpose: extended multi-step reasoning over a task
+   - Input: a task description or problem statement
+   - Output: a structured plan with steps and reasoning
+   - Example: `/ultraplan refactor this module to use async/await`
+2. **Navigation** — `/teleport <symbol-or-path>`
+   - Purpose: quickly jump to a file or function by name
+   - Input: a symbol name (function, class, struct) or file path
+   - Output: the file content with that symbol highlighted
+   - Example: `/teleport UserService`, `/teleport src/auth.rs`
+3. **Code Analysis** — `/bughunter [scope]`
+   - Purpose: scan the codebase for likely bugs or issues
+   - Input: optional scope (e.g., "src/handlers", "lib.rs")
+   - Output: list of suspicious patterns with explanations
+   - Example: `/bughunter src`, `/bughunter` (entire workspace)
+
+**Acceptance:** Each command has a one-line description, a practical example, and expected behavior documented.
+
+**Blocker:** None. Pure documentation.
+
+**Source:** Clawhip nudge 2026-04-21 21:47 KST — discovered discrepancy between `claw --help` and USAGE.md coverage.