refactor: consolidate triplicated CSV/text loop-task expansion in process.py (#1957)

* refactor: consolidate triplicated CSV/text loop-task expansion in process.py

This consolidates three near-identical implementations of CSV/text-file
loop-task expansion onto the existing _create_loop_subtasks() helper:

- Enhanced _create_loop_subtasks() with optional decision_mode parameter
- Replaced inline start-task logic (lines 1116-1205) with helper call
- Replaced inline mid-workflow logic (lines 1273-1330) with helper call

Removes ~300 lines of duplicated logic and fixes latent CSV-parsing
inconsistency where inline copies used plain csv.reader() instead of
csv.reader(f, quotechar='"', escapechar='\\').

All loop feature behavior preserved: CSV/text files, decision-task
creation with inherited next_tasks, and sync/async paths work identically.

Fixes #1953

Co-authored-by: MervinPraison <MervinPraison@users.noreply.github.com>

* fix: resolve critical issues in loop task consolidation

- Fix lexicographic sorting that breaks ordering with 10+ subtasks
- Retire parent loop task after expansion to prevent completion blocking
- Replace placeholder task names in decision conditions with concrete names
- Use is_start flag instead of name sorting for proper subtask selection

Addresses reviewer feedback from Greptile and CodeRabbit on PR #1957

Co-authored-by: Mervin Praison <MervinPraison@users.noreply.github.com>

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Co-authored-by: praisonai-triage-agent[bot] <272766704+praisonai-triage-agent[bot]@users.noreply.github.com>
Co-authored-by: MervinPraison <MervinPraison@users.noreply.github.com>

Author: praisonai-triage-agent[bot]