perf(gateway): tune Telegram cadence + adaptive fast-path for short replies

Re-authored against current main from PR #10388 by @wilsen0.  The
original branch is 3800+ commits stale and could not be cherry-picked
without reverting unrelated work; this change carries only the perf
intent forward.

Tuning summary
==============

Text-batch ingress (gateway/platforms/telegram.py):
  - HERMES_TELEGRAM_TEXT_BATCH_DELAY_SECONDS default 0.6 -> 0.3
  - HERMES_TELEGRAM_TEXT_BATCH_SPLIT_DELAY_SECONDS default 2.0 -> 1.0
  - Adaptive fast-path tiers in _flush_text_batch:
      total <= 320 cp -> min(cap, 0.18)
      total <= 1024 cp -> min(cap, 0.24)
      else            -> cap
    A single short reply now reaches the agent in ~180ms instead of
    600ms.  Tier constants compose with the configured cap via min()
    so an operator who tightens HERMES_TELEGRAM_TEXT_BATCH_DELAY_SECONDS
    below 0.18 still wins on every tier.
  - _env_float_clamped helper replaces bare float(os.getenv()).
    Rejects NaN / Inf, applies optional min/max bounds.  Used for
    text-batch + media-batch knobs.  Prevents asyncio.sleep(NaN)
    crashes when an operator typos an env var.

Stream cadence (gateway/config.py + stream_consumer.py):
  - StreamingConfig.edit_interval default 1.0s -> 0.8s
  - StreamingConfig.buffer_threshold default 40 -> 24 chars
  - DEFAULT_STREAMING_EDIT_INTERVAL / BUFFER_THRESHOLD / CURSOR are now
    a single source of truth.  StreamConsumerConfig imports them
    instead of duplicating the literals; the prior dual-source drift
    is fixed.

Tool progress (gateway/display_config.py):
  - Telegram default tool_progress 'all' -> 'new'.  Inside
    Telegram's ~1 edit/s flood envelope the 'all' default would
    accumulate edit pressure on busy chats; 'new' shows only the
    leading bubble per tool batch and feels less spammy.
  - Slack tier_low override (tool_progress='off') is preserved.

Composition with native draft streaming (#23512)
================================================

The mid-stream cadence (edit_interval, buffer_threshold) gates BOTH
the draft path (send_draft) and the edit path (edit_message), so the
tighter cadence helps native draft as much as edit-based.  The
text-batch fast-path applies before the consumer starts, so it speeds
up the first-token latency on every transport.  No conflict.

Stale-base avoidance
====================

Re-authored from scratch rather than cherry-picked.  Dropped from the
original branch:
  - Unrelated d2f043f9c 'fix(anthropic): preserve third-party thinking
    continuity' commit
  - boot_md.py builtin gateway hook (unrelated)
  - Reverted Slack tool_progress='off' (#14663) restoration
  - Reverted Platform plugin discovery, MSGRAPH_WEBHOOK, YUANBAO
    members deletion
  - 2300+ lines of run.py base-skew noise

Tests
=====

New tests/gateway/test_telegram_text_batch_perf.py:
  - 7 tests for _env_float_clamped (NaN, Inf, garbage, bounds).
  - 4 tests for the adaptive-tier composition rules.

Updated tests/gateway/test_display_config.py:
  - test_platform_default_when_no_user_config: 'all' -> 'new' for
    Telegram, with comment.
  - test_high_tier_platforms: split into Telegram-overrides-to-new
    and Discord-stays-all assertions.

Closes #10388.

Co-authored-by: wilsen0 <132184373+wilsen0@users.noreply.github.com>

gateway/display_config.py

@@ -81,7 +81,7 @@ _TIER_MINIMAL = {
 
 _PLATFORM_DEFAULTS: dict[str, dict[str, Any]] = {
     # Tier 1 — full edit support, personal/team use
-    "telegram":    _TIER_HIGH,
+    "telegram":    {**_TIER_HIGH, "tool_progress": "new"},
     "discord":     _TIER_HIGH,
 
     # Tier 2 — edit support, often customer/workspace channels