docs: simplify upgrade SOP for AI agent execution

[thepagent]

Summary

Replaces the verbose upgrade SOP (~600 lines) with a streamlined guide (~260 lines) designed for AI agent execution.

Before vs After

	Before	After
Lines	~600	~260
Backup steps	7 separate steps	3 items (values, secret, $HOME)
Verification gates	Multiple with exit codes	1 simple check
Rollback	helm rollback + manual PVC restore	Uninstall → fresh install → restore
Human gates	2 (pre-release + post-upgrade)	None — agent decides from smoke test
Pod label selector	app.kubernetes.io/name=$DEPLOYMENT (wrong)	app.kubernetes.io/component=kiro (correct)

Design principles

1. Agent-first — every step is a concrete command, no ambiguous instructions
2. Self-healing — failure at any point has a defined recovery path
3. Minimal — 3 things to backup, 1 command to upgrade, 1 test to decide

Key improvements

• Uses -f values.yaml (not --reuse-values) to avoid Helm: discord.enabled not set on upgrade from 0.7.6 causes CrashLoopBackOff #383 (missing discord.enabled on upgrade)
• Uninstall + fresh install rollback is simpler than helm rollback which doesn't revert PVC data anyway
• Version override built into the flow (supports both stable and beta targets)
• Fixed pod label selector that was broken in the original SOP

Flow

RESOLVE → BACKUP → UPGRADE → SMOKE TEST → DONE ✅
                                    ↓ fail
                               ROLLBACK
                          (uninstall → reinstall → restore)

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