chore: consolidate documentation, archive superseded planning docs

The repo had accumulated 20 root-level .md files (multiple architecture
versions, master spec, opus implementation guide, status docs from May 5)
and 35+ docs/ files mixing canonical references with stale planning notes.
Recent commits had moved the project well past the state those docs
described.

Changes:
  - Move 19 pre-rebuild root docs to docs/archive/ (architecture v1/v2.1/
    v2.2, master spec, opus guide, phases, status, README pitch). Pre-
    served because they show the architectural conversation; not
    authoritative anymore.
  - Move 17 stale docs/ files to docs/archive/ (alignment report, May 6
    handoff, interface planning trio, tool-system design rounds,
    subagent investigation, sea-consciousness analysis, sexy-ui, tui
    enhancement guides, sensorium questions).
  - Move 34 superseded task scopes to docs/tasks/archive/ (scope-1/2/3
    landed, tool-system phases 1-4 superseded, all 10 tui-component
    tasks completed, n1-four-fold / aster-rebuild / n25-four-elements
    folded into scope-3/4 and N+1 LLM pass, port-compaction superseded
    by in-session-compaction-implementation).
  - Delete 5 .bak files (ASTER_ARCHITECTURE, CONSCIOUSNESS_CYCLE,
    energy-topology, scope-3-n1-consciousness x2).
  - Delete docs/FIMEG_REFERENCE.md (byte-identical duplicate of
    reference/Fimeg.md; the NOTE TO OPUS header belongs in reference/).
  - Delete 3 .txt session captures (harnesstime, massive,
    "souveraine updates") and souveraine.log; add log to .gitignore.
  - Delete orphan src/core/persona/mod.rs (~220 LOC referencing the
    ~/.pi/unified/ paths from the TypeScript precursor; never exported
    in core/mod.rs; the persona-router-completion task survives so the
    goal isn't lost).
  - Rewrite README.md to reflect the actual current state instead of
    the May 5 pitch.
  - Rewrite docs/INDEX.md as a navigable map of the canonical set plus
    a pointer at the archive.

Active state after this commit:
  - root: README.md, Cargo.toml/lock, souveraine.toml(.example), src/,
    docs/, saf/, reference/, examples/, tauri/, web/, target/, .gitignore.
  - docs/: 14 canonical docs (THE_QUESTION, CONTEXT_CONSTITUTION,
    SENSORIUM_ARCHITECTURE, ASTER_ARCHITECTURE, CONSCIOUSNESS_CYCLE,
    DECISIONS, MEMORY_BLOCKS_DECISION, CRON_API_AUTH, FEDERATION_SKETCH,
    ARCHITECTURE_v3, HANDOFF_NEXT, SCOPED_WORK_PLAN, PROJECT_STATE_ANALYSIS,
    INDEX) + archive/ (36 files).
  - docs/tasks/: 15 active scopes + archive/ (34 files).
  - cargo build: 0 errors, 145 pre-existing warnings (unchanged).

.gitignore

@@ -48,3 +48,4 @@ config.local.toml
 
 # Web assets (if present)
 web/dist/
+souveraine.log