docs: roll README + CHANGELOG forward past v0.3.1

README:
- Status line bumped from v0.3.0 to v0.3.1 with the actually-validated
  framing (K8s Ready under QEMU virt+HVF, CoreDNS + local-path +
  nginx all Running) and a link to CHANGELOG.md for full notes.
- Roadmap: Phase 7 (generic ARM64) flipped to "Complete (v0.3.1, K8s
  Ready under QEMU virt+HVF)". OCI cosign verification, LABEL=KSOLODATA
  on ARM64, and real-hardware ARM64 validation move from "Planned for
  v0.3.1" to "Planned for v0.3.2" — they didn't make this release.

CHANGELOG:
- New "[Unreleased]" section covering the four post-v0.3.1 CI / repo
  housekeeping commits: drop tag trigger on build-arm64.yaml (04a5cd2),
  gitignore .env/credentials (48267e1), fix gated x86 job staying
  "queued" instead of "skipped" (fb24e64), and paths-ignore on
  build-arm64.yaml so workflow/docs-only commits skip the 60-minute
  kernel rebuild (e1b8a69).

No runtime changes.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -5,6 +5,39 @@ All notable changes to KubeSolo OS are documented in this file.
 Format based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 versioning follows [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+Pure CI / repository housekeeping; no runtime changes since v0.3.1. All
+items below shake out workflow-loop bugs exposed by the v0.3.1 release
+flow on Gitea Actions.
+
+### Fixed (CI)
+
+- `build-arm64.yaml` no longer triggers on tag pushes. `release.yaml`
+  already produces the ARM64 disk image as part of the release flow, so
+  triggering both on the same tag wasted an hour of Odroid runner time
+  on a duplicate kernel build. (`04a5cd2`)
+- The gated `build-iso-amd64` job in `release.yaml` (`if: false` until an
+  amd64-linux runner exists) used to advertise `runs-on: amd64-linux`.
+  With no matching runner, Gitea left the job queued forever and the
+  overall workflow run never transitioned to `success` — even though
+  every load-bearing job had finished and the release was already
+  published. Now uses `runs-on: ubuntu-latest` so any runner picks the
+  job up just long enough to evaluate `if: false` and mark it `skipped`.
+  (`fb24e64`)
+- `build-arm64.yaml` now ignores workflow-file, docs, and `*.md` changes
+  via `paths-ignore` (`.gitea/workflows/**`, `.github/workflows/**`,
+  `docs/**`, top-level `*.md`, `.gitignore`). Workflow- / docs-only
+  commits no longer kick off a 60-minute kernel rebuild on the Odroid.
+  Any change to a kernel fragment, init script, or build script still
+  triggers the full build, as intended. (`e1b8a69`)
+
+### Changed
+
+- `.gitignore` now excludes `.env`, `.env.*`, `*.token`, `*.pat` to keep
+  Gitea PATs and other credentials used during release ops from being
+  accidentally committed. (`48267e1`)
+
 ## [0.3.1] - 2026-05-15
 
 First fully-functional generic ARM64 release. v0.3.0 shipped the build