fix(development-planning): remove round floor and repo-only agent check

Two residues in plan-implementation that undercut the Opus 5 migration:

- Quick Process step 3 mandated "2-3 rounds" while the ceiling table
  below caps Simple at 1 and Medium at 2. The numbered step reads as an
  instruction, so the floor survived the removal. It now defers to the
  table.
- The agent-existence check grepped `packages/plugins/*/agents/`, a path
  that exists only in this repo. In a consumer repo it matches nothing,
  and the adjacent "fails at dispatch" warning then reads as "do not
  dispatch" - a self-disabling guard. Replaced with the session's own
  agent inventory, plus the naming rule stated as fact (frontmatter
  `name:`, `-agent` suffix, cross-plugin `plugin-name:agent-name`).

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

Author: wkoutre

packages/plugins/development-planning/skills/plan-implementation/SKILL.md

@@ -22,7 +22,7 @@ Create clear, actionable implementation plans through collaborative multi-agent
 
 1. **Analyze Context**: Understand the task, leverage any prior exploration
 2. **Select Agents**: Choose specialists for the dimensions the task actually raises, up to 10
-3. **Collaborative Discussion**: 2-3 rounds of multi-agent refinement
+3. **Collaborative Discussion**: Multi-agent refinement, up to the round ceiling in the table below
 4. **Synthesize Plan**: Generate comprehensive implementation plan
 5. **Output File**: Write plan to `.claude-output/plan-[timestamp].md`
 

packages/plugins/development-planning/skills/plan-implementation/planning-guide.md

@@ -20,12 +20,15 @@ Select agents based on technical domains in the task. The names below are the di
 | External research        | `researcher-agent`                              |
 | Debugging                | `debug-assistant-agent`                         |
 
-Before dispatching an agent that is not in this table, confirm it exists - a name that does not
-match an agent's frontmatter `name:` fails at dispatch:
-
-```bash
-grep -rhE '^name: ' packages/plugins/*/agents/ | sort -u
-```
+Before dispatching an agent that is not in this table, confirm it appears in the agent inventory
+available in the current session - the agent types listed in your own context are the authoritative
+set, and a name that is not among them fails at dispatch. Do not try to verify a name by searching
+the filesystem: these agents ship from installed plugins rather than from the user's project, so a
+repo-relative search returns nothing even when the agent is available.
+
+Dispatch names come from an agent's frontmatter `name:` field; marketplace agents carry an `-agent`
+suffix. Agents from a different plugin are addressed as `plugin-name:agent-name`, for example
+`development-codebase-tools:security-analyzer-agent`.
 
 ### By Complexity