cleanup(storage): phase 4 retire legacy path/config helpers after normalization

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Summary

Phase 3 should leave AccessiWeather with one active runtime storage contract. After that, we should clean up the parallel legacy path/config machinery that still exists in the repo.

This issue is intentionally after storage-root normalization, not before.

Phase 4 goal

Retire legacy path/config/state helpers that are no longer part of the active runtime model, while preserving read compatibility where needed.

In scope

1) Remove or quarantine legacy path callers/helpers

Audit and clean up:

• src/accessiweather/config_utils.py
• src/accessiweather/location.py
• src/accessiweather/notifications/weather_notifier.py
• src/accessiweather/logging_config.py
• any tests that only validate deprecated get_config_dir() / old storage semantics

Expected result:

• one obvious path for storage resolution in the codebase
• no active module silently writing to old .accessiweather / ad hoc roots
• no dead persistence paths left looking authoritative

2) Trim compatibility fallbacks that were only needed during refactor rollout

Examples:

• old legacy-path fallbacks once Phase 3 has shipped safely
• duplicate startup/path logic that exists only to bridge old codepaths

3) Align docs/tests with the actual storage model

Update only the docs/tests that still describe or assert stale behavior, especially around:

• portable mode markers / layout
• config/cache/log/state locations
• migration expectations

Optional pre-work / soak gate

Before closing this issue, do one short observation pass on a real installed build and a portable build to confirm:

• Phase 3 path routing is stable
• no surprise writes happen outside the canonical root
• old users are not losing config/state across upgrade

Out of scope

• new product features
• re-architecting unrelated config models
• changing alert/runtime-state schema beyond removing dead compatibility code
• aggressive cleanup of historical docs that are not user/developer facing

Done looks like

• engineers no longer need to ask whether a module should use Paths, config_utils.get_config_dir(), or ConfigManager.config_dir
• the answer is obvious from one canonical storage helper / contract