Improve schedule UX with time semantics and credential error consistency

[pentaoa]

Summary

Improves sustech-cli UX for agents and headless users based on real usage feedback:

1. Full ISO-8601 schedule timestamps: Personal schedule entries from week-specific queries now include complete startAt/endAt datetimes (e.g. 2026-09-15T14:00:00+08:00) combining class date with period-based clock times. Agents can answer "this afternoon" queries without reassembling date + time themselves.

2. Date-based schedule queries: tis schedule --date YYYY-MM-DD resolves the teaching week from the academic calendar automatically, enabling natural queries like "where is class on 2026-09-15?"

3. Structured room fields: When multiple rooms are detected (e.g. "505, 506"), a rooms array is populated alongside the primary room field for compatibility.

4. Credential error consistency: Linux encrypted-file backend now produces stable error codes (MASTER_PASSWORD_REQUIRED, MASTER_PASSWORD_INVALID) with consistent remediation across auth status, doctor, and credential reads. No more generic store errors when master password is missing or incorrect.

5. Official period mapping documentation: docs/ARCHITECTURE.md now documents the SUSTech period→clock time mapping as a single source of truth for humans and agents.

Changes

Schedule Timestamps (Maintainer Feedback Addressed)

• ✅ Full ISO-8601 datetimes instead of bare HH:MM
• ✅ Only week-specific personal schedule queries get timestamps (via --week, --date, or current-week)
• ✅ Catalog schedule[] slots lack concrete dates → keep period fields only
• ✅ Enrichment happens in CLI layer with calendar context
• ✅ periodStart/periodEnd retained for compatibility

Implementation

• Add enrichScheduleEntriesWithDatetimes() taking teachingStartDate + week
• Calculate concrete date for each entry based on teaching week + weekday
• Generate full Asia/Shanghai ISO-8601 timestamps: YYYY-MM-DDTHH:MM:SS+08:00
• Only enrich entries scheduled for the query week
• Support --date YYYY-MM-DD on tis schedule command
• Parse multiple rooms from comma/semicolon-separated room strings
• Throw MASTER_PASSWORD_REQUIRED/INVALID from encrypted store with remediation
• Update credentialStatusReasonCode to recognize all master password error codes

Documentation

• docs/ARCHITECTURE.md: Period mapping table + ISO timestamp behavior
• docs/AUTHENTICATION.md: Encrypted-file error codes and remediation
• CHANGELOG.md: Full summary of all changes
• FEATURE_DEMO.md: Updated with ISO datetime examples

Testing

• All 474 tests pass
• 6 new tests for schedule enrichment, timestamps, room parsing
• Fixed bitmap week parsing test data

Hard constraints met

✅ No new top-level convenience commands added
✅ Existing commands (tis schedule, auth status, doctor) enriched
✅ Backward compatible: period fields retained, new fields are optional/additive
✅ ISO datetimes only for concrete date contexts (personal schedule with week)
✅ Catalog slots keep period-only format (no fake dates)
✅ Tests green, small reviewable PR
✅ FEATURE_DEMO.md kept and updated

Related

Addresses feedback from headless Linux usage and agent query patterns where:

• "where is class this afternoon?" required both date lookup and period math
• Master password errors showed as generic store failures without clear remediation
• Multiple lab rooms in descriptions were unparseable
• Bare clock times needed date reassembly for datetime comparisons