fix(docker): install cached custom starter on container restart

[wezell]

Summary

• The Docker init script 40-custom-starter-zip.sh only exported DOT_STARTER_DATA_LOAD inside the download branch, so a cached starter zip was never applied on restart.
• Moved the export to run whenever the cached file exists and is non-empty, so cached starters install on every boot.
• Quoted path expansions to satisfy shellcheck.

Fixes #35788

Test plan

• Start container with CUSTOM_STARTER_URL set → fresh download, starter installed.
• Restart container with cached zip on disk → no re-download, starter still installed (DOT_STARTER_DATA_LOAD exported).
• Failed/zero-byte download is cleaned up and no starter export occurs.

🤖 Generated with Claude Code

[claude]

Claude finished @wezell's task in 50s —— View job

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Rollback Safety Analysis

• Read rollback-unsafe categories reference
• Reviewed PR diff (433ea3e1...6961919c)
• Analyzed diff against every unsafe category
• Applied label

Verdict: ✅ Safe To Rollback

Files changed (1):

• dotCMS/src/main/docker/original/ROOT/srv/40-custom-starter-zip.sh (Docker init script, +15/-13)

Category review:

Category	Match?
C-1 Structural Data Model	No — no DB or schema changes
C-2 ES Mapping	No — no ES changes
C-3 Content JSON Model Version	No — no CURRENT_MODEL_VERSION bump
C-4 DROP TABLE/COLUMN	No — no DDL
H-1 One-Way Data Migration	No — no data backfill
H-2 RENAME TABLE/COLUMN	No
H-3 Primary Key Restructuring	No
H-4 New Field Type	No
H-5 Binary Storage Provider	No — this is the starter-zip download cache (/data/shared/dotcms-starter-*.zip), not FileStorageAPIImpl or StoragePersistenceProvider
H-6 DROP PROCEDURE/FUNCTION	No
H-7 NOT NULL column	No
M-1 Column Type Change	No
M-2 Push Publishing Bundle	No
M-3 REST/GraphQL API Contract	No
M-4 OSGi Plugin API	No

Why it is safe: The change is confined to a container startup shell script that decides whether to set DOT_STARTER_DATA_LOAD based on the presence of a cached starter zip. It does not alter any database schema, Elasticsearch mapping, JSON model version, API contract, or OSGi-exposed interface. Rolling back to the previous container image restores the prior shell-script behavior with no data or runtime consequences — the cached zip on disk remains readable by either version.

Label AI: Safe To Rollback applied.
• fix/custom-starter-cached-install