chore: gitignore + untrack mars-genesis planning docs, scrub CHANGELOG

The mars-genesis-v2-plan-phase1.md, mars-genesis-v2-plan-phase2.md,
and mars-genesis-v3-plan.md files at the top of docs/ were superpowers
planning artifacts that got placed at a public path by mistake.
Gitignored under docs/mars-genesis-v*-plan*.md and untracked via
git rm --cached. Working copies stay on the local disk.

Also scrubbed bracket-link superpowers references from CHANGELOG.md
(plain-text "Spec: docs/superpowers/..." commit-body lines, plus the
"##### Spec" sub-section that linked to the brain-storage abstraction
spec). Remaining superpowers mentions in CHANGELOG are commit
subjects describing what a commit did (e.g. "gitignore superpowers")
which are historical and not links to internal docs.

Author: jddunn

.gitignore

@@ -31,3 +31,6 @@ coverage/
 # Superpowers
 .superpowers/
 docs/superpowers/
+
+# Internal planning docs (superpowers workflow)
+docs/mars-genesis-v*-plan*.md

CHANGELOG.md

@@ -477,8 +477,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -955,8 +953,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -1431,8 +1427,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -1905,8 +1899,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -2377,8 +2369,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -2845,8 +2835,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -3310,8 +3298,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -3772,8 +3758,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -4231,8 +4215,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -4688,8 +4670,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -5143,8 +5123,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -5596,8 +5574,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -6047,8 +6023,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.2.0 (2026-04-30)
 
@@ -6496,8 +6470,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## <small>0.5.10 (2026-04-30)</small>
 
@@ -6681,8 +6653,6 @@ Brain.open(path), Brain.create(path), Memory.create({path}) all removed.
 Postgres deployments require brainId on every brain operation. Existing
 SQLite files auto-migrate on first open.
 
-Spec: docs/superpowers/specs/2026-04-26-brain-storage-abstraction-design.md
-Plan: docs/superpowers/plans/2026-04-26-brain-storage-abstraction-plan.md
 
 ## 0.3.0 (2026-04-26)