fix(helm): decouple [discord] section from botToken presence

[thepagent]

Issue

Closes #392.
Supersedes #393 (rebased onto current main, removed stale/duplicate Slack section, updated values.yaml).

Reason for this change

The [discord] block in config.toml is conditionally rendered only when ($cfg.discord).botToken is non-empty. This forces users who manage secrets at runtime (e.g., AWS Secrets Manager → K8s Secret → env var) to either:

1. Pass a dummy token to Helm (confusing)
2. Pass the real token to Helm (stored in Helm release history — security risk)

The template already hardcodes bot_token = "${DISCORD_BOT_TOKEN}" as a placeholder for runtime expansion, so requiring botToken in Helm values serves no purpose other than gating the block.

Description of changes

configmap.yaml (one-line change):

- {{- if and (ne (toString ($cfg.discord).enabled) "false") ($cfg.discord).botToken }}
+ {{- if ($cfg.discord).enabled }}

values.yaml:

• Removed botToken from the kiro agent discord section (no longer needed at render time)
• Updated comment to explain runtime token injection via DISCORD_BOT_TOKEN env var
• Added enabled: true to all commented-out agent examples (claude, opencode, cursor) so users see the correct pattern

⚠️ Breaking Change

This changes the discord condition from opt-out (enabled defaults to true unless "false") to opt-in (enabled must be explicitly true).

Who is affected: Users who have discord.botToken set but never explicitly set discord.enabled: true. After this change, their [discord] block will not render.

Migration: Add discord.enabled: true to your agent's discord values.

Context

• Discord discussion: https://discord.com/channels/1491295327620169908/1491365162869985283
• Reference: feat(helm): add pod extensibility controls #380