feat(project): unique COMPOSE_PROJECT_NAME in .env for Docker volumes

[RoboShyim (roboshyim)]

Summary

Implements #1251.

Docker Compose was using the directory basename as the project name, so named volumes (db-data, …) collided when a project folder was deleted and recreated with the same name (or two trees shared a basename). That made system:is-installed succeed against stale DB data and skip the install wizard.

Changes

Area	Behaviour
project create --docker	Writes COMPOSE_PROJECT_NAME=sw-<basename>-<6hex> to host .env (not .env.local)
Non-docker create	.env stays empty
Existing projects	Unset → basename behaviour (backward compatible); already set → left alone
flexmigrator.MigrateEnv	Keeps COMPOSE_PROJECT_NAME in the new empty .env when splitting flex env
Migration wizard → Docker	EnsureComposeProjectName if missing

Compose still runs with Dir = projectRoot (devtui/compose.go) and picks up .env automatically — no -p / compose name: key required.

Tests

• go test ./internal/shop/ ./internal/flexmigrator/ ./internal/devtui/ -run Migration…
• Scaffold docker vs non-docker, uniqueness of same basename, flex preserve, Ensure* preserve/append

Checklist

• project create --docker writes unique name to .env
• Two creates with same folder name get different names
• Non-docker does not require a project name
• Tests for scaffold docker vs non-docker
• Migration wizard path sets name if missing

[Codecov Comments Bot (codecov-commenter)]

Codecov Report

❌ Patch coverage is 79.16667% with 15 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.71%. Comparing base (3340b47) to head (083ad74).

Files with missing lines	Patch %	Lines
internal/shop/compose_project_name.go	82.00%	9 Missing ⚠️
internal/devtui/model_update.go	20.00%	4 Missing ⚠️
internal/flexmigrator/env.go	92.30%	1 Missing ⚠️
internal/shop/project_scaffold.go	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1252      +/-   ##
==========================================
+ Coverage   53.63%   53.71%   +0.07%     
==========================================
  Files         303      304       +1     
  Lines       23325    23392      +67     
==========================================
+ Hits        12511    12564      +53     
- Misses      10787    10801      +14     
  Partials       27       27              

Flag	Coverage Δ
go-test	53.71% <79.16%> (+0.07%)	⬆️

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