[explorer] feat: display transfer messages in transaction details view

[cryptoBeliever]

Summary

• Display NEM transfer messages correctly in the transaction details view (plain text, hex-prefixed, encrypted).
• Update tests and fixtures to use numeric message type

Motivation

Transfer message presentation depends on whether a message is plain or encrypted. The REST API exposes type as a numeric; the frontend applies formatting rules:

• type=1, no fe prefix → decode hex payload to UTF-8
• type=1, fe prefix → show as HEX: <payload>
• type=2 → show encrypted payload as-is with a dedicated label

Depends on

• lightapi PR merged and published

Issue: #2352

SQL migration

BEGIN;

UPDATE transactions
SET payload = jsonb_set(
	payload::jsonb,
	'{message}',
	((payload::jsonb->'message')::jsonb - 'is_plain'::text)
	|| jsonb_build_object('type', (payload::jsonb->'message'->'is_plain')::jsonb),
	true
)
WHERE payload IS NOT NULL
	AND (payload::jsonb ? 'message')
	AND ((payload::jsonb->'message')::jsonb ? 'is_plain')
	AND NOT ((payload::jsonb->'message')::jsonb ? 'type');

-- Remove legacy key when both are present.
UPDATE transactions
SET payload = jsonb_set(
	payload::jsonb,
	'{message}',
	(payload::jsonb->'message')::jsonb - 'is_plain'::text,
	true
)
WHERE payload IS NOT NULL
	AND (payload::jsonb ? 'message')
	AND ((payload::jsonb->'message')::jsonb ? 'is_plain')
	AND ((payload::jsonb->'message')::jsonb ? 'type');

COMMIT;

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.95%. Comparing base (bbe0fe4) to head (7889a96).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #2383      +/-   ##
==========================================
+ Coverage   95.44%   96.95%   +1.51%     
==========================================
  Files         657      276     -381     
  Lines       51116    21313   -29803     
  Branches     1359      206    -1153     
==========================================
- Hits        48786    20664   -28122     
+ Misses       2282      643    -1639     
+ Partials       48        6      -42     

Flag	Coverage Δ
explorer-frontend	94.93% <100.00%> (+0.05%)	⬆️
explorer-puller	?
explorer-rest	?
wallet-mobile-symbol	?

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
explorer/frontend/api/transactions.js	100.00% <100.00%> (ø)
explorer/frontend/utils/common.js	99.73% <100.00%> (+0.56%)	⬆️

... and 381 files with indirect coverage changes

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