fix(#479): share one followable network-FS remedy (the ~/.tracebloc advice couldn't work)

[shujaatTracebloc]

#479 — _pf_storage_type's network-FS remedy was un-followable

On a network filesystem, _pf_storage_type told operators:

Fix: point HOST_DATA_DIR at a LOCAL disk — the default ~/.tracebloc is local:
HOST_DATA_DIR="$HOME/.tracebloc" ./install-k8s.sh

But on a network HOME, ~/.traceblocis NFS (the very problem), and validate_config rejects paths outside$HOME — so the printed fix could never work. early_data_dir_guard (from #441) already had a followable remedy for exactly this case.

Fix: extract the followable remedy into a shared _pf_network_fs_remedy and use it from both_pf_storage_type and early_data_dir_guard, so they can't drift. It names the options that actually work:

1. install as a user whose home is on a local disk (ask your admin), or
2. TRACEBLOC_ALLOW_NETWORK_FS=1 to proceed anyway (not recommended — the DB can corrupt),

and notes datasets may stay on network storage via HOST_DATASET_DIR.

Tests

_pf_storage_type NFS now prints the followable remedy and not the old ~/.tracebloc advice; a consistency test asserts both callers emit the same remedy. shellcheck --severity=error + check-style + check-drift clean; full preflight.bats green (81); scripts/manifest.sha256 regenerated (R8).

Closes#479

---

Note

Low Risk
Operator-facing hint text only in install preflight; behavior unchanged aside from clearer remediation, with bats coverage.

Overview
Fixes misleading preflight guidance when HOST_DATA_DIR sits on NFS/CIFS: _pf_storage_type used to suggest HOST_DATA_DIR="$HOME/.tracebloc", which is still network-backed on a network home and cannot be fixed with a path outside $HOME per validate_config.

Introduces _pf_network_fs_remedy with actionable options (local-home user, or TRACEBLOC_ALLOW_NETWORK_FS=1) and a note that HOST_DATASET_DIR may stay on network storage. early_data_dir_guard and _pf_storage_type both call it so operator text cannot drift.

Tests assert the NFS failure path shows the new remedy and not the old ~/.tracebloc line; scripts/manifest.sha256 is updated for preflight.sh.

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[LukasWodka]

/fr-pass