fix: detect and prevent Helm float64 mangling of Discord channel IDs (closes #43)

[thepagent]

Problem

Discord Snowflake IDs are 19-digit integers (> 2^53). Helm --set parses them as float64, losing precision and rendering them in scientific notation (e.g. 1.2345678901234568e+18). This causes agent-broker to silently ignore all messages.

Changes

1. templates/configmap.yaml — fail-fast validation

{{- if regexMatch "e\\+|E\\+" (toString .) }}
{{- fail "discord.allowedChannels contains a mangled ID — use --set-string" }}
{{- end }}

If a channel ID contains scientific notation, helm install/upgrade fails immediately with a clear error message instead of silently deploying a broken config.

2. templates/NOTES.txt — post-install warning

Shows --set-string usage reminder on every install/upgrade.

3. values.yaml — inline comment

Documents the --set-string requirement next to allowedChannels.

Before vs After

╔══════════════════════════════════════════════════════════════════════╗
║                      BEFORE (silent failure) 💀                      ║
╠══════════════════════════════════════════════════════════════════════╣
║                                                                      ║
║  User runs:                                                          ║
║  helm install ... --set discord.allowedChannels[0]=1234567890123456789
║                                                                      ║
║  ┌─────────────┐     ┌──────────────┐     ┌──────────────────┐       ║
║  │ Helm --set  │────▶│ float64 cast │────▶│ configmap.yaml   │       ║
║  │             │     │ precision 💥 │     │                  │       ║
║  └─────────────┘     └──────────────┘     │ allowed_channels │       ║
║                                           │ = ["1.23456789e+18"]     ║
║  1234567890123456789                      └────────┬─────────┘       ║
║  → 1.2345678901234568e+18                          │                 ║
║  → NEVER matches real ID                           ▼                 ║
║                                           ┌──────────────────┐       ║
║                                           │ agent-broker     │       ║
║                                           │ ignores ALL msgs │       ║
║                                           │ 🤷 no error log  │       ║
║                                           └──────────────────┘       ║
╠══════════════════════════════════════════════════════════════════════╣
║                      AFTER (fail fast) 🛡️                            ║
╠══════════════════════════════════════════════════════════════════════╣
║                                                                      ║
║  ❌ helm install ... --set discord.allowedChannels[0]=123...789       ║
║                                                                      ║
║  ┌─────────────┐     ┌──────────────┐     ┌──────────────────┐       ║
║  │ Helm --set  │────▶│ float64 cast │────▶│ configmap.yaml   │       ║
║  │             │     │ precision 💥 │     │ regexMatch "e+"  │       ║
║  └─────────────┘     └──────────────┘     │ ⛔ FAIL:         │       ║
║                                           │ "mangled ID,     │       ║
║                                           │  use --set-string"│      ║
║                                           └──────────────────┘       ║
║                                                                      ║
║  ✅ helm install ... --set-string discord.allowedChannels[0]="123..."
║                                                                      ║
║  ┌─────────────┐     ┌──────────────┐     ┌──────────────────┐       ║
║  │ --set-string│────▶│ kept as      │────▶│ configmap.yaml   │       ║
║  │             │     │ string ✅    │     │                  │       ║
║  └─────────────┘     └──────────────┘     │ allowed_channels │       ║
║                                           │ = ["123456789.."]│       ║
║                                           └────────┬─────────┘       ║
║                                                    ▼                 ║
║                                           ┌──────────────────┐       ║
║                                           │ agent-broker     │       ║
║                                           │ matches! ✅      │       ║
║                                           │ 🎉 msgs received │       ║
║                                           └──────────────────┘       ║
╚══════════════════════════════════════════════════════════════════════╝

Testing

# This will now FAIL with a helpful error:
helm template test . --set discord.allowedChannels[0]=1234567890123456789

# This works correctly:
helm template test . --set-string discord.allowedChannels[0]="1234567890123456789"

Closes #43