Introducing our main agent: Sisyphus (#113)

* docs: rename OmO agent to Sisyphus, OmO-Plan to Planner-Sisyphus

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* refactor: rename OmO agent to Sisyphus with automatic config migration

- Rename OmO agent to Sisyphus (uses mythological pushing-the-boulder concept)
- Rename OmO-Plan to Planner-Sisyphus for consistency
- Update config schema: omo_agent → sisyphus_agent
- Add backward compatibility: automatically migrate user's oh-my-opencode.json files
- Migration handles old keys (OmO, omo, OmO-Plan, omo-plan) and rewrites config when detected
- Update agent name mappings, index files, and type definitions
- Add Sisyphus PNG asset to brand identity

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* docs: add Sisyphus mythology introduction and teammates concept to all READMEs

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* feat(startup-toast): show Sisyphus steering message when enabled

- Updated startup toast to show "Sisyphus on steroids is steering OpenCode" when Sisyphus agent is enabled
- Refactored getToastMessage function to handle conditional message rendering
- Pass isSisyphusEnabled flag from plugin configuration to auto-update-checker hook

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* docs(sisyphus): add philosophical context to Sisyphus agent identity

- Add "Why Sisyphus?" explanation connecting the daily work cycle of humans and AI agents
- Emphasize code quality expectations: indistinguishable from senior engineer's work
- Concise identity statement: work, delegate, verify, ship without AI slop

This clarifies the agent's purpose and reinforces the principle that quality code should not reveal whether it was written by human or AI.

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src/agents/index.ts

@@ -1,5 +1,5 @@
 import type { AgentConfig } from "@opencode-ai/sdk"
-import { omoAgent } from "./omo"
+import { sisyphusAgent } from "./sisyphus"
 import { oracleAgent } from "./oracle"
 import { librarianAgent } from "./librarian"
 import { exploreAgent } from "./explore"
@@ -8,7 +8,7 @@ import { documentWriterAgent } from "./document-writer"
 import { multimodalLookerAgent } from "./multimodal-looker"
 
 export const builtinAgents: Record<string, AgentConfig> = {
-  OmO: omoAgent,
+  Sisyphus: sisyphusAgent,
   oracle: oracleAgent,
   librarian: librarianAgent,
   explore: exploreAgent,