feat(engram): add data-directory domain core

[tonyblu331]

Linked Issue

Closes #346

PR Type

• type:feature - Engram data-dir feature slice

Maintainer action required: add the type:feature label. GitHub rejected label updates from tonyblu331 with AddLabelsToLabelable permission errors.

Summary

Adds the core Engram data-directory domain helpers now that the disk-space infrastructure slice (#638) is merged into main.

This slice keeps the chain reviewable: it only introduces default/custom data-dir references, database path helpers, copy behavior, environment overrides, and presentation helpers. It deliberately does not include service orchestration, location listing, TUI state, install-flow wiring, or unrelated Windows test stabilization.

Changes

Area	What changed
internal/components/engram/copy.go	Adds database copy behavior with destination validation and parent creation.
internal/components/engram/env.go	Adds environment-driven data-dir override helpers.
internal/components/engram/presenter.go	Adds user-facing formatting for data-dir paths.
Tests	Covers copy behavior, env override behavior, and presenter formatting.

Test Plan

Focused Local Unit Tests

GOCACHE=G:\codex-go-tmp\gocache GOTMPDIR=G:\codex-go-tmp\gotmp TEMP=G:\codex-go-tmp\tmp TMP=G:\codex-go-tmp\tmp APPDATA=G:\codex-go-tmp\appdata XDG_CONFIG_HOME=G:\codex-go-tmp\xdg go test -count=1 ./internal/components/engram ./internal/storage

Full Suite / CI

• Focused local tests pass for this slice (./internal/components/engram, ./internal/storage).
• GitHub Actions Unit Tests pass on PR feat(engram): add data-directory domain core #700.
• GitHub Actions E2E Tests pass on PR feat(engram): add data-directory domain core #700 (ubuntu, fedora, arch).
• GitHub Actions PR validation passes for issue reference, issue approval, and cognitive load.
• GitHub Actions type:* label check passes — pending maintainer-applied type:feature label.

Local Windows full-suite note

I did not broaden this PR to fix unrelated local Windows baseline failures. I re-ran go test -count=1 ./... from an LF checkout to avoid CRLF golden noise; it still fails locally in packages outside this slice. The same targeted failures reproduce on current origin/main (1f13b8d), so they are not caused by this PR:

Package	Local failure
internal/cli	TestRunInstallKimiMissingUVFailsBeforeExecutingInstallCommands
internal/components/gga	TestInjectIsIdempotent / first-run config-change expectation
internal/update	TestCheckSingleTool_EngramUsesBinaryReleaseChannel
internal/update/upgrade	TestConfigPathsForBackup_GGAExtrasAreIncluded

Those should be handled in a separate Windows test-stabilization PR if maintainers want local Windows go test ./... green. This slice stays scoped to Engram data-dir domain helpers.

Chain Context

Field	Value
Chain strategy	Sequential upstream slices unless a maintainer creates upstream chain branches
Chain start	feat/engram-dd-1-infra (#638, merged)
Chain end	fix/engram-dd-15-operation-consistency
Current slice	feat/engram-dd-2-domain-core
Prior dependency	#638 merged into main at 2026-05-27 13:01:52 UTC
Follow-up branch	feat/engram-dd-3-domain-service after this slice lands
Review budget	357 changed lines
Out of scope	Service orchestration, location listing, TUI state/screens, app wiring, unrelated Windows full-suite stabilization, and later hardening/test slices

Planned review order by branch:

main -> feat/engram-dd-1-infra (#638 merged) -> 📍 feat/engram-dd-2-domain-core -> feat/engram-dd-3-domain-service -> feat/engram-dd-4-domain-locations -> feat/engram-dd-5-model-screens -> feat/engram-dd-6-tui-flow-consolidated -> fix/engram-dd-7-service-hardening -> feat/engram-dd-8-app-wiring-consolidated -> fix/engram-dd-9-test-stabilization -> fix/engram-dd-10-mcp-env-sync -> fix/engram-dd-11-data-dir-consistency -> fix/engram-dd-12-rollback-consistency -> fix/engram-dd-13-mcp-config-preservation -> test/engram-dd-14-mcp-config-preservation -> fix/engram-dd-15-operation-consistency

Contributor Checklist

• PR is linked to an issue with status:approved
• PR stays within 400 changed lines
• Exactly one type:* label is applied (type:feature, maintainer action required)
• Focused local unit tests pass
• GitHub Actions Unit Tests pass
• GitHub Actions E2E Tests pass (ubuntu, fedora, arch)
• Documentation update not required for this internal domain slice
• My commits follow Conventional Commits format
• My commits do not include Co-Authored-By trailers