fix(config): allow Sisyphus-Junior agent customization via oh-my-opencode.json (#648)

* fix(config): allow Sisyphus-Junior agent customization via oh-my-opencode.json

Allow users to configure Sisyphus-Junior agent via agents["Sisyphus-Junior"]
in oh-my-opencode.json, removing hardcoded defaults while preserving safety
constraints.
Closes #623
Changes:
- Add "Sisyphus-Junior" to AgentOverridesSchema and OverridableAgentNameSchema
- Create createSisyphusJuniorAgentWithOverrides() helper with guardrails
- Update config-handler to use override helper instead of hardcoded values
- Fix README category wording (runtime presets, not separate agents)
Honored override fields:
- model, temperature, top_p, tools, permission, description, color, prompt_append
Safety guardrails enforced post-merge:
- mode forced to "subagent" (cannot change)
- prompt is append-only (base discipline text preserved)
- blocked tools (task, sisyphus_task, call_omo_agent) always denied
- disable: true ignores override block, uses defaults
Category interaction:
- sisyphus_task(category=...) runs use the base Sisyphus-Junior agent config
- Category model/temperature overrides take precedence at request time
- To change model for a category, set categories.<cat>.model (not agent override)
- Categories are runtime presets applied to Sisyphus-Junior, not separate agents
Tests: 15 new tests in sisyphus-junior.test.ts, 3 new schema tests

Co-Authored-By: Sisyphus <sisyphus@mengmota.com>

* test(sisyphus-junior): add guard assertion for prompt anchor text

Add validation that baseEndIndex is not -1 before using it for ordering
assertion. Previously, if "Dense > verbose." text changed in the base
prompt, indexOf would return -1 and any positive appendIndex would pass.

Co-Authored-By: Sisyphus <sisyphus@mengmota.com>

---------

Co-authored-by: Sisyphus <sisyphus@mengmota.com>

README.md

@@ -1058,7 +1058,7 @@ Configure concurrency limits for background agent tasks. This controls how many
 
 ### Categories
 
-Categories enable domain-specific task delegation via the `sisyphus_task` tool. Each category pre-configures a specialized `Sisyphus-Junior-{category}` agent with optimized model settings and prompts.
+Categories enable domain-specific task delegation via the `sisyphus_task` tool. Each category applies runtime presets (model, temperature, prompt additions) when calling the `Sisyphus-Junior` agent.
 
 **Default Categories:**