DOCFIX-175/176: OpenTofu state file security + VR1 teardown/rollback runbook ...

Found while reviewing what's missing from the VR1 buildout ahead of
tomorrow's execution.

DOCFIX-175: terraform.tfstate stores sensitive=true variables (like
maas_api_key) in plaintext regardless of the flag, which only redacts
CLI/plan output (verified against HashiCorp's own docs). Added .gitignore
coverage, a "State file handling" section in opentofu/README.md, an inline
caveat on maas_api_key's description, and a "SECURE THE STATE FILE" callout
at Stage 1 Step 10 -- the actual first real tofu apply (an early draft
wrongly assumed Stage 3; corrected after reading the runbooks directly).

DOCFIX-176: new runbooks/dc-dc-teardown-rollback.md for the OpenTofu/
libvirt/MAAS-vm_host layer, which D-061's existing teardown scripts don't
cover (different layer, juju/MAAS-machine). Two paths (scoped -target
teardown or full VR1 destroy), a rollback decision tree favoring
fix-forward over destroy, and explicit mesh-link shared-infrastructure
handling.

Also folded in: a fix to docs/changelog-20260710-ledger-scan-self-inflicted-falsepositive-fix.md
after re-running ledger-scan.sh caught that its own narration (and the
session-ledger mirror) had reintroduced the exact false-positive class
DOCFIX-174 had just fixed.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QrcJx8TUar7pYAvpGJw57A

DOCFIX-154/155/156: Stage 2/3/5 runbooks -- Office1 standup, DC substrate, per-DC bundle ...

Three DC-DC runbooks authored in parallel this evening:
- Stage 2 (Office1 headend standup): MAAS-region/NetBox/GitBucket/Tailscale,
  each VM-creation step forking an explicit OpenTofu-blocked vs manual-debt
  path rather than picking one silently. Flags a real gap: no Office1-local
  network is modeled in opentofu/.
- Stage 3 (OpenTofu builds each DC substrate): DC1-first, DC2 hard-gated on
  NetBox literals. Walks every open decision (node sizing, MAAS zone/pool,
  config.xml tokens, netem params) and stops rather than inventing values.
- Stage 5 (Juju controller + bundle, per DC): describes adapting the
  existing phase-01..08 loop to run twice, not duplicating it. Mandates the
  $DC selector convention (DOCFIX-151) before every adapted command block.
  Surfaces the undesigned IPv6 family-matrix overlay as blocking work.

All three: not yet executed (prep-only session, no live infrastructure
reachable tonight); repo-lint 0 fail/1 documented warn.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01QrcJx8TUar7pYAvpGJw57A