archive: remove entire archive/ directory and all references

archive/ contained the old narrative wiki (superseded by DB as source
of truth), hermes-plans, oikos-cards, ledger, secrets-issuance, and
SOPS backups — all Python-era artifacts with no ongoing value.

Updated all cross-references in:
- AGENTS.md, README.md
- .agents/operations/commands.md (point to docs/infrastructure/)
- .agents/shared/llm-wiki.md, page-templates.md
- .agents/domains/knowledge/schema.md, operations/schema.md
- .agents/skills/*/SKILL.md
- docs/infrastructure/*.md (removed archive link targets)
- docs-lint/SKILL.md known-baseline note

.agents/shared/page-templates.md

@@ -118,7 +118,7 @@ What it looks like after.
 Changelog entries to write, index status to update.
 ```
 
-### Investigation (`investigation` entity in the DB; historically `archive/knowledge/sources/investigations/YYYY-MM-DD-slug.md`)
+### Investigation (`investigation` entity in the DB; historically in `archive/knowledge/sources/investigations/`, now deleted)
 
 ```markdown
 # YYYY-MM-DD — <title>